[PATCH 0/2] eliminate some section start symbols

[PATCH 0/2] eliminate some section start symbols

[Jan Beulich]

Section start symbols frequently obscure the actual symbol name living
at the start of the section. Eliminate them where they can be replaced
by linker resolved .startof.* symbols. (Section end symbols may have
the same undesirable effect, but they're less easy to eliminate, as
they'd need to be represented by the sum of .startof.<section> and
.sizeof.<section>).

1: x86: force suitable alignment in sources rather than in linker script
2: make use of .startof.() and .sizeof.() assembler expressions

Signed-off-by: Jan Beulich <jbeulich@suse.com>


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[PATCH 1/2] x86: force suitable alignment in sources rather than in linker script

[Jan Beulich]

[-- Attachment #1: Type: text/plain, Size: 2420 bytes --]

Besides being more logical this also allows verifying correct recording
of alignments in .o files.

The cpu0_stack related ASSERT() in xen.lds.S is now of questionable
value (as it now verifies correct tool chain behavior), but I've left
it in nevertheless.

Signed-off-by: Jan Beulich <jbeulich@suse.com>

--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -89,6 +89,7 @@ struct hvm_function_table hvm_funcs __re
  */
 #define HVM_IOBITMAP_SIZE (3 * PAGE_SIZE)
 unsigned long __section(".bss.page_aligned")
+    __attribute__((aligned(PAGE_SIZE)))
     hvm_io_bitmap[HVM_IOBITMAP_SIZE / BYTES_PER_LONG];
 
 /* Xen command-line option to enable HAP */
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -125,7 +125,8 @@
 #include <asm/pci.h>
 
 /* Mapping of the fixmap space needed early. */
-l1_pgentry_t __section(".bss.page_aligned") l1_fixmap[L1_PAGETABLE_ENTRIES];
+l1_pgentry_t __section(".bss.page_aligned") __attribute__((aligned(PAGE_SIZE)))
+    l1_fixmap[L1_PAGETABLE_ENTRIES];
 
 #define MEM_LOG(_f, _a...) gdprintk(XENLOG_WARNING , _f "\n" , ## _a)
 
@@ -588,7 +589,8 @@ static inline void guest_get_eff_kern_l1
     TOGGLE_MODE();
 }
 
-const char __section(".bss.page_aligned.const") zero_page[PAGE_SIZE];
+const char __section(".bss.page_aligned.const")
+    __attribute__((aligned(PAGE_SIZE))) zero_page[PAGE_SIZE];
 
 static void invalidate_shadow_ldt(struct vcpu *v, int flush)
 {
--- a/xen/arch/x86/setup.c
+++ b/xen/arch/x86/setup.c
@@ -105,7 +105,8 @@ unsigned long __read_mostly xen_virt_end
 
 DEFINE_PER_CPU(struct tss_struct, init_tss);
 
-char __section(".bss.stack_aligned") cpu0_stack[STACK_SIZE];
+char __section(".bss.stack_aligned") __attribute__((aligned(STACK_SIZE)))
+    cpu0_stack[STACK_SIZE];
 
 struct cpuinfo_x86 __read_mostly boot_cpu_data = { 0, 0, 0, 0, -1 };
 
--- a/xen/arch/x86/xen.lds.S
+++ b/xen/arch/x86/xen.lds.S
@@ -222,7 +222,6 @@ SECTIONS
   } :text
 
   .data : {                    /* Data */
-       . = ALIGN(PAGE_SIZE);
        *(.data.page_aligned)
        *(.data)
        *(.data.rel)
@@ -231,10 +230,8 @@ SECTIONS
   } :text
 
   .bss : {                     /* BSS */
-       . = ALIGN(STACK_SIZE);
        __bss_start = .;
        *(.bss.stack_aligned)
-       . = ALIGN(PAGE_SIZE);
        *(.bss.page_aligned*)
        *(.bss)
        . = ALIGN(SMP_CACHE_BYTES);




[-- Attachment #2: x86-bss-align.patch --]
[-- Type: text/plain, Size: 2487 bytes --]

x86: force suitable alignment in sources rather than in linker script

Besides being more logical this also allows verifying correct recording
of alignments in .o files.

The cpu0_stack related ASSERT() in xen.lds.S is now of questionable
value (as it now verifies correct tool chain behavior), but I've left
it in nevertheless.

Signed-off-by: Jan Beulich <jbeulich@suse.com>

--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -89,6 +89,7 @@ struct hvm_function_table hvm_funcs __re
  */
 #define HVM_IOBITMAP_SIZE (3 * PAGE_SIZE)
 unsigned long __section(".bss.page_aligned")
+    __attribute__((aligned(PAGE_SIZE)))
     hvm_io_bitmap[HVM_IOBITMAP_SIZE / BYTES_PER_LONG];
 
 /* Xen command-line option to enable HAP */
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -125,7 +125,8 @@
 #include <asm/pci.h>
 
 /* Mapping of the fixmap space needed early. */
-l1_pgentry_t __section(".bss.page_aligned") l1_fixmap[L1_PAGETABLE_ENTRIES];
+l1_pgentry_t __section(".bss.page_aligned") __attribute__((aligned(PAGE_SIZE)))
+    l1_fixmap[L1_PAGETABLE_ENTRIES];
 
 #define MEM_LOG(_f, _a...) gdprintk(XENLOG_WARNING , _f "\n" , ## _a)
 
@@ -588,7 +589,8 @@ static inline void guest_get_eff_kern_l1
     TOGGLE_MODE();
 }
 
-const char __section(".bss.page_aligned.const") zero_page[PAGE_SIZE];
+const char __section(".bss.page_aligned.const")
+    __attribute__((aligned(PAGE_SIZE))) zero_page[PAGE_SIZE];
 
 static void invalidate_shadow_ldt(struct vcpu *v, int flush)
 {
--- a/xen/arch/x86/setup.c
+++ b/xen/arch/x86/setup.c
@@ -105,7 +105,8 @@ unsigned long __read_mostly xen_virt_end
 
 DEFINE_PER_CPU(struct tss_struct, init_tss);
 
-char __section(".bss.stack_aligned") cpu0_stack[STACK_SIZE];
+char __section(".bss.stack_aligned") __attribute__((aligned(STACK_SIZE)))
+    cpu0_stack[STACK_SIZE];
 
 struct cpuinfo_x86 __read_mostly boot_cpu_data = { 0, 0, 0, 0, -1 };
 
--- a/xen/arch/x86/xen.lds.S
+++ b/xen/arch/x86/xen.lds.S
@@ -222,7 +222,6 @@ SECTIONS
   } :text
 
   .data : {                    /* Data */
-       . = ALIGN(PAGE_SIZE);
        *(.data.page_aligned)
        *(.data)
        *(.data.rel)
@@ -231,10 +230,8 @@ SECTIONS
   } :text
 
   .bss : {                     /* BSS */
-       . = ALIGN(STACK_SIZE);
        __bss_start = .;
        *(.bss.stack_aligned)
-       . = ALIGN(PAGE_SIZE);
        *(.bss.page_aligned*)
        *(.bss)
        . = ALIGN(SMP_CACHE_BYTES);

[-- Attachment #3: Type: text/plain, Size: 127 bytes --]

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[PATCH 2/2] make use of .startof.() and .sizeof.() assembler expressions

[Jan Beulich]

[-- Attachment #1: Type: text/plain, Size: 11427 bytes --]

Section start symbols frequently obscure the actual symbol name living
at the start of the section. Eliminate them where they can be replaced
by linker resolved .startof.* symbols. (Section end symbols may have
the same undesirable effect, but they're less easy to eliminate, as
they'd need to be represented by the sum of .startof.<section> and
.sizeof.<section>).

Along those lines use .sizeof.* where section sizes get calculated
from the difference of section and and section start symbols.

Note that this would be nice for the build-id section too, but:
- The generated (by ld) section names differ between ELF and COFF/PE
  (ELF: .note.gnu.build-id; COFF/PE[2.26+]: .buildid), yet we compile
  version.c just once (and hence can use only either of the necessary
  .startof./.sizeof. forms).
- The ELF section name needs to be quoted in the .startof./.sizeof.
  expressions, yet that quoting is supported only by gas 2.26+.

Signed-off-by: Jan Beulich <jbeulich@suse.com>

--- a/xen/arch/arm/arm32/head.S
+++ b/xen/arch/arm/arm32/head.S
@@ -184,10 +184,10 @@ hyp:    PRINT("- Xen starting in Hyp mod
         bne   skip_bss
 
         PRINT("- Zero BSS -\r\n")
-        ldr   r0, =__bss_start       /* Load start & end of bss */
-        ldr   r1, =__bss_end
+        ldr   r0, =.startof.(.bss)   /* Load start & size of bss */
+        ldr   r1, =.sizeof.(.bss)
         add   r0, r0, r10            /* Apply physical offset */
-        add   r1, r1, r10
+        add   r1, r1, r0             /* Calculate end of bss */
 
         mov   r2, #0
 1:      str   r2, [r0], #4
--- a/xen/arch/arm/arm64/head.S
+++ b/xen/arch/arm/arm64/head.S
@@ -318,10 +318,10 @@ el2:    PRINT("- Xen starting at EL2 -\r
         cbnz  x22, skip_bss
 
         PRINT("- Zero BSS -\r\n")
-        ldr   x0, =__bss_start       /* Load start & end of bss */
-        ldr   x1, =__bss_end
+        ldr   x0, =.startof.(.bss)   /* Load start & size of bss */
+        ldr   x1, =.sizeof.(.bss)
         add   x0, x0, x20            /* Apply physical offset */
-        add   x1, x1, x20
+        add   x1, x1, x0             /* Calculate end of .bss */
 
 1:      str   xzr, [x0], #8
         cmp   x0, x1
--- a/xen/arch/arm/device.c
+++ b/xen/arch/arm/device.c
@@ -21,8 +21,8 @@
 #include <xen/errno.h>
 #include <xen/lib.h>
 
-extern const struct device_desc _sdevice[], _edevice[];
-extern const struct acpi_device_desc _asdevice[], _aedevice[];
+extern const struct device_desc _sdevice[] asm(".startof.(.dev.info)");
+extern const struct device_desc _edevice[];
 
 int __init device_init(struct dt_device_node *dev, enum device_class class,
                        const void *data)
@@ -51,6 +51,11 @@ int __init device_init(struct dt_device_
     return -EBADF;
 }
 
+#ifdef CONFIG_ACPI
+
+extern const struct acpi_device_desc _asdevice[] asm(".startof.(.adev.info)");
+extern const struct acpi_device_desc _aedevice[];
+
 int __init acpi_device_init(enum device_class class, const void *data, int class_type)
 {
     const struct acpi_device_desc *desc;
@@ -68,6 +73,8 @@ int __init acpi_device_init(enum device_
     return -EBADF;
 }
 
+#endif
+
 enum device_class device_get_class(const struct dt_device_node *dev)
 {
     const struct device_desc *desc;
--- a/xen/arch/arm/domain_build.c
+++ b/xen/arch/arm/domain_build.c
@@ -2058,7 +2058,7 @@ static void __init find_gnttab_region(st
      * enough space for a large grant table
      */
     kinfo->gnttab_start = __pa(_stext);
-    kinfo->gnttab_size = (_etext - _stext) & PAGE_MASK;
+    kinfo->gnttab_size = _sizeof_text & PAGE_MASK;
 
     /* Make sure the grant table will fit in the region */
     if ( (kinfo->gnttab_size >> PAGE_SHIFT) < max_grant_frames )
--- a/xen/arch/arm/platform.c
+++ b/xen/arch/arm/platform.c
@@ -22,7 +22,8 @@
 #include <xen/init.h>
 #include <asm/psci.h>
 
-extern const struct platform_desc _splatform[], _eplatform[];
+extern const struct platform_desc _splatform[] asm(".startof.(.arch.info)");
+extern const struct platform_desc _eplatform[];
 
 /* Pointer to the current platform description */
 static const struct platform_desc *platform;
--- a/xen/arch/arm/xen.lds.S
+++ b/xen/arch/arm/xen.lds.S
@@ -31,7 +31,6 @@ SECTIONS
   . = XEN_VIRT_START;
   _start = .;
   .text : /* XXX should be AT ( XEN_PHYS_START ) */ {
-        _stext = .;            /* Text section */
        *(.text)
        *(.text.cold)
        *(.text.unlikely)
@@ -42,7 +41,6 @@ SECTIONS
 
   . = ALIGN(PAGE_SIZE);
   .rodata : {
-        _srodata = .;          /* Read-only data */
         /* Bug frames table */
        __start_bug_frames = .;
        *(.bug_frames.0)
@@ -104,21 +102,18 @@ SECTIONS
 
   . = ALIGN(8);
   .arch.info : {
-      _splatform = .;
       *(.arch.info)
       _eplatform = .;
   } :text
 
   . = ALIGN(8);
   .dev.info : {
-      _sdevice = .;
       *(.dev.info)
       _edevice = .;
   } :text
 
   . = ALIGN(8);
   .adev.info : {
-      _asdevice = .;
       *(.adev.info)
       _aedevice = .;
   } :text
@@ -126,7 +121,6 @@ SECTIONS
   . = ALIGN(PAGE_SIZE);             /* Init code and data */
   __init_begin = .;
   .init.text : {
-       _sinittext = .;
        *(.init.text)
        _einittext = .;
   } :text
@@ -174,7 +168,6 @@ SECTIONS
   __init_end = .;
 
   .bss : {                     /* BSS */
-       __bss_start = .;
        *(.bss.stack_aligned)
        . = ALIGN(PAGE_SIZE);
        *(.bss.page_aligned)
@@ -186,7 +179,6 @@ SECTIONS
        *(.bss.percpu.read_mostly)
        . = ALIGN(SMP_CACHE_BYTES);
        __per_cpu_data_end = .;
-       __bss_end = .;
   } :text
   _end = . ;
 
--- a/xen/arch/x86/boot/head.S
+++ b/xen/arch/x86/boot/head.S
@@ -124,9 +124,8 @@ __start:
         mov     %eax,sym_phys(multiboot_ptr)
 
         /* Initialize BSS (no nasty surprises!) */
-        mov     $sym_phys(__bss_start),%edi
-        mov     $sym_phys(__bss_end),%ecx
-        sub     %edi,%ecx
+        mov     $sym_phys(.startof.(.bss)),%edi
+        mov     $.sizeof.(.bss),%ecx
         xor     %eax,%eax
         shr     $2,%ecx
         rep stosl
--- a/xen/arch/x86/setup.c
+++ b/xen/arch/x86/setup.c
@@ -181,7 +181,7 @@ void __init discard_initial_images(void)
     initial_images = NULL;
 }
 
-extern char __init_begin[], __init_end[], __bss_start[], __bss_end[];
+extern char __init_begin[], __init_end[], __bss_end[];
 
 static void __init init_idle_domain(void)
 {
--- a/xen/arch/x86/tboot.c
+++ b/xen/arch/x86/tboot.c
@@ -48,7 +48,7 @@ static uint64_t __initdata sinit_base, _
 #define TXTCR_HEAP_BASE             0x0300
 #define TXTCR_HEAP_SIZE             0x0308
 
-extern char __init_begin[], __bss_start[], __bss_end[];
+extern char __init_begin[];
 
 #define SHA1_SIZE      20
 typedef uint8_t   sha1_hash_t[SHA1_SIZE];
@@ -376,7 +376,12 @@ void tboot_shutdown(uint32_t shutdown_ty
                                               __pa(&_stext);
         /* bss */
         g_tboot_shared->mac_regions[2].start = (uint64_t)__pa(&__bss_start);
-        g_tboot_shared->mac_regions[2].size = __pa(&__bss_end) - __pa(&__bss_start);
+#if 0 /* This doesn't work due to -fPIC. */
+        g_tboot_shared->mac_regions[2].size = _sizeof_bss;
+#else
+        asm ( "movl $.sizeof.(.bss),%0"
+              : "=m" (g_tboot_shared->mac_regions[2].size) );
+#endif
 
         /*
          * MAC domains and other Xen memory
--- a/xen/arch/x86/xen.lds.S
+++ b/xen/arch/x86/xen.lds.S
@@ -58,7 +58,6 @@ SECTIONS
   . = __XEN_VIRT_START + MB(1);
   _start = .;
   .text : {
-        _stext = .;            /* Text and read-only data */
        *(.text)
        *(.text.cold)
        *(.text.unlikely)
@@ -77,7 +76,6 @@ SECTIONS
 
   __2M_rodata_start = .;       /* Start of 2M superpages, mapped RO. */
   .rodata : {
-       _srodata = .;
        /* Bug frames table */
        . = ALIGN(4);
        __start_bug_frames = .;
@@ -149,7 +147,6 @@ SECTIONS
   . = ALIGN(PAGE_SIZE);             /* Init code and data */
   __init_begin = .;
   .init.text : {
-       _sinittext = .;
        *(.init.text)
        /*
         * Here are the replacement instructions. The linker sticks them
@@ -230,7 +227,6 @@ SECTIONS
   } :text
 
   .bss : {                     /* BSS */
-       __bss_start = .;
        *(.bss.stack_aligned)
        *(.bss.page_aligned*)
        *(.bss)
@@ -323,5 +319,5 @@ ASSERT(IS_ALIGNED(__init_end,   PAGE_SIZ
 
 ASSERT(IS_ALIGNED(trampoline_start, 4), "trampoline_start misaligned")
 ASSERT(IS_ALIGNED(trampoline_end,   4), "trampoline_end misaligned")
-ASSERT(IS_ALIGNED(__bss_start,      4), "__bss_start misaligned")
-ASSERT(IS_ALIGNED(__bss_end,        4), "__bss_end misaligned")
+ASSERT(IS_ALIGNED(.startof..bss,    4), ".bss misaligned")
+ASSERT(IS_ALIGNED(.sizeof..bss,     4), ".bss size misaligned")
--- a/xen/include/xen/kernel.h
+++ b/xen/include/xen/kernel.h
@@ -71,24 +71,34 @@ extern char _start[], _end[], start[];
     (__p >= _start) && (__p < _end);            \
 })
 
-extern char _stext[], _etext[];
+extern const char _stext[] asm(".startof.(.text)");
+extern const char _etext[];
 #define is_kernel_text(p) ({                    \
     char *__p = (char *)(unsigned long)(p);     \
     (__p >= _stext) && (__p < _etext);          \
 })
 
-extern const char _srodata[], _erodata[];
+extern const char _sizeof_text[] asm(".sizeof.(.text)");
+#define _sizeof_text ((unsigned long)_sizeof_text)
+
+extern const char _srodata[] asm(".startof.(.rodata)");
+extern const char _erodata[];
 #define is_kernel_rodata(p) ({                  \
     const char *__p = (const char *)(unsigned long)(p);     \
     (__p >= _srodata) && (__p < _erodata);      \
 })
 
-extern char _sinittext[], _einittext[];
+extern const char _sinittext[] asm(".startof.(.init.text)");
+extern const char _einittext[];
 #define is_kernel_inittext(p) ({                \
     char *__p = (char *)(unsigned long)(p);     \
     (__p >= _sinittext) && (__p < _einittext);  \
 })
 
+extern char __bss_start[] asm(".startof.(.bss)");
+extern const char _sizeof_bss[] asm(".sizeof.(.bss)");
+#define _sizeof_bss ((unsigned long)_sizeof_bss)
+
 extern enum system_state {
     SYS_STATE_early_boot,
     SYS_STATE_boot,
--- a/xen/tools/symbols.c
+++ b/xen/tools/symbols.c
@@ -143,11 +143,12 @@ static int read_symbol(FILE *in, struct
 		sym++;
 
 	/* Ignore most absolute/undefined (?) symbols. */
-	if (strcmp(sym, "_stext") == 0)
+	if (strcmp(sym, "_stext") == 0 || strcmp(sym, ".startof..text") == 0)
 		_stext = s->addr;
 	else if (strcmp(sym, "_etext") == 0)
 		_etext = s->addr;
-	else if (strcmp(sym, "_sinittext") == 0)
+	else if (strcmp(sym, "_sinittext") == 0 ||
+		 strcmp(sym, ".startof..init.text") == 0)
 		_sinittext = s->addr;
 	else if (strcmp(sym, "_einittext") == 0)
 		_einittext = s->addr;
@@ -168,6 +169,9 @@ static int read_symbol(FILE *in, struct
 	/* exclude also MIPS ELF local symbols ($L123 instead of .L123) */
 	else if (str[0] == '$')
 		goto skip_tail;
+	/* Also strip .startof. symbols. */
+	if (strncmp(sym, ".startof.", 9) == 0)
+		goto skip_tail;
 
 	/* include the type field in the symbol name, so that it gets
 	 * compressed together */



[-- Attachment #2: startof.patch --]
[-- Type: text/plain, Size: 11487 bytes --]

make use of .startof.() and .sizeof.() assembler expressions

Section start symbols frequently obscure the actual symbol name living
at the start of the section. Eliminate them where they can be replaced
by linker resolved .startof.* symbols. (Section end symbols may have
the same undesirable effect, but they're less easy to eliminate, as
they'd need to be represented by the sum of .startof.<section> and
.sizeof.<section>).

Along those lines use .sizeof.* where section sizes get calculated
from the difference of section and and section start symbols.

Note that this would be nice for the build-id section too, but:
- The generated (by ld) section names differ between ELF and COFF/PE
  (ELF: .note.gnu.build-id; COFF/PE[2.26+]: .buildid), yet we compile
  version.c just once (and hence can use only either of the necessary
  .startof./.sizeof. forms).
- The ELF section name needs to be quoted in the .startof./.sizeof.
  expressions, yet that quoting is supported only by gas 2.26+.

Signed-off-by: Jan Beulich <jbeulich@suse.com>

--- a/xen/arch/arm/arm32/head.S
+++ b/xen/arch/arm/arm32/head.S
@@ -184,10 +184,10 @@ hyp:    PRINT("- Xen starting in Hyp mod
         bne   skip_bss
 
         PRINT("- Zero BSS -\r\n")
-        ldr   r0, =__bss_start       /* Load start & end of bss */
-        ldr   r1, =__bss_end
+        ldr   r0, =.startof.(.bss)   /* Load start & size of bss */
+        ldr   r1, =.sizeof.(.bss)
         add   r0, r0, r10            /* Apply physical offset */
-        add   r1, r1, r10
+        add   r1, r1, r0             /* Calculate end of bss */
 
         mov   r2, #0
 1:      str   r2, [r0], #4
--- a/xen/arch/arm/arm64/head.S
+++ b/xen/arch/arm/arm64/head.S
@@ -318,10 +318,10 @@ el2:    PRINT("- Xen starting at EL2 -\r
         cbnz  x22, skip_bss
 
         PRINT("- Zero BSS -\r\n")
-        ldr   x0, =__bss_start       /* Load start & end of bss */
-        ldr   x1, =__bss_end
+        ldr   x0, =.startof.(.bss)   /* Load start & size of bss */
+        ldr   x1, =.sizeof.(.bss)
         add   x0, x0, x20            /* Apply physical offset */
-        add   x1, x1, x20
+        add   x1, x1, x0             /* Calculate end of .bss */
 
 1:      str   xzr, [x0], #8
         cmp   x0, x1
--- a/xen/arch/arm/device.c
+++ b/xen/arch/arm/device.c
@@ -21,8 +21,8 @@
 #include <xen/errno.h>
 #include <xen/lib.h>
 
-extern const struct device_desc _sdevice[], _edevice[];
-extern const struct acpi_device_desc _asdevice[], _aedevice[];
+extern const struct device_desc _sdevice[] asm(".startof.(.dev.info)");
+extern const struct device_desc _edevice[];
 
 int __init device_init(struct dt_device_node *dev, enum device_class class,
                        const void *data)
@@ -51,6 +51,11 @@ int __init device_init(struct dt_device_
     return -EBADF;
 }
 
+#ifdef CONFIG_ACPI
+
+extern const struct acpi_device_desc _asdevice[] asm(".startof.(.adev.info)");
+extern const struct acpi_device_desc _aedevice[];
+
 int __init acpi_device_init(enum device_class class, const void *data, int class_type)
 {
     const struct acpi_device_desc *desc;
@@ -68,6 +73,8 @@ int __init acpi_device_init(enum device_
     return -EBADF;
 }
 
+#endif
+
 enum device_class device_get_class(const struct dt_device_node *dev)
 {
     const struct device_desc *desc;
--- a/xen/arch/arm/domain_build.c
+++ b/xen/arch/arm/domain_build.c
@@ -2058,7 +2058,7 @@ static void __init find_gnttab_region(st
      * enough space for a large grant table
      */
     kinfo->gnttab_start = __pa(_stext);
-    kinfo->gnttab_size = (_etext - _stext) & PAGE_MASK;
+    kinfo->gnttab_size = _sizeof_text & PAGE_MASK;
 
     /* Make sure the grant table will fit in the region */
     if ( (kinfo->gnttab_size >> PAGE_SHIFT) < max_grant_frames )
--- a/xen/arch/arm/platform.c
+++ b/xen/arch/arm/platform.c
@@ -22,7 +22,8 @@
 #include <xen/init.h>
 #include <asm/psci.h>
 
-extern const struct platform_desc _splatform[], _eplatform[];
+extern const struct platform_desc _splatform[] asm(".startof.(.arch.info)");
+extern const struct platform_desc _eplatform[];
 
 /* Pointer to the current platform description */
 static const struct platform_desc *platform;
--- a/xen/arch/arm/xen.lds.S
+++ b/xen/arch/arm/xen.lds.S
@@ -31,7 +31,6 @@ SECTIONS
   . = XEN_VIRT_START;
   _start = .;
   .text : /* XXX should be AT ( XEN_PHYS_START ) */ {
-        _stext = .;            /* Text section */
        *(.text)
        *(.text.cold)
        *(.text.unlikely)
@@ -42,7 +41,6 @@ SECTIONS
 
   . = ALIGN(PAGE_SIZE);
   .rodata : {
-        _srodata = .;          /* Read-only data */
         /* Bug frames table */
        __start_bug_frames = .;
        *(.bug_frames.0)
@@ -104,21 +102,18 @@ SECTIONS
 
   . = ALIGN(8);
   .arch.info : {
-      _splatform = .;
       *(.arch.info)
       _eplatform = .;
   } :text
 
   . = ALIGN(8);
   .dev.info : {
-      _sdevice = .;
       *(.dev.info)
       _edevice = .;
   } :text
 
   . = ALIGN(8);
   .adev.info : {
-      _asdevice = .;
       *(.adev.info)
       _aedevice = .;
   } :text
@@ -126,7 +121,6 @@ SECTIONS
   . = ALIGN(PAGE_SIZE);             /* Init code and data */
   __init_begin = .;
   .init.text : {
-       _sinittext = .;
        *(.init.text)
        _einittext = .;
   } :text
@@ -174,7 +168,6 @@ SECTIONS
   __init_end = .;
 
   .bss : {                     /* BSS */
-       __bss_start = .;
        *(.bss.stack_aligned)
        . = ALIGN(PAGE_SIZE);
        *(.bss.page_aligned)
@@ -186,7 +179,6 @@ SECTIONS
        *(.bss.percpu.read_mostly)
        . = ALIGN(SMP_CACHE_BYTES);
        __per_cpu_data_end = .;
-       __bss_end = .;
   } :text
   _end = . ;
 
--- a/xen/arch/x86/boot/head.S
+++ b/xen/arch/x86/boot/head.S
@@ -124,9 +124,8 @@ __start:
         mov     %eax,sym_phys(multiboot_ptr)
 
         /* Initialize BSS (no nasty surprises!) */
-        mov     $sym_phys(__bss_start),%edi
-        mov     $sym_phys(__bss_end),%ecx
-        sub     %edi,%ecx
+        mov     $sym_phys(.startof.(.bss)),%edi
+        mov     $.sizeof.(.bss),%ecx
         xor     %eax,%eax
         shr     $2,%ecx
         rep stosl
--- a/xen/arch/x86/setup.c
+++ b/xen/arch/x86/setup.c
@@ -181,7 +181,7 @@ void __init discard_initial_images(void)
     initial_images = NULL;
 }
 
-extern char __init_begin[], __init_end[], __bss_start[], __bss_end[];
+extern char __init_begin[], __init_end[], __bss_end[];
 
 static void __init init_idle_domain(void)
 {
--- a/xen/arch/x86/tboot.c
+++ b/xen/arch/x86/tboot.c
@@ -48,7 +48,7 @@ static uint64_t __initdata sinit_base, _
 #define TXTCR_HEAP_BASE             0x0300
 #define TXTCR_HEAP_SIZE             0x0308
 
-extern char __init_begin[], __bss_start[], __bss_end[];
+extern char __init_begin[];
 
 #define SHA1_SIZE      20
 typedef uint8_t   sha1_hash_t[SHA1_SIZE];
@@ -376,7 +376,12 @@ void tboot_shutdown(uint32_t shutdown_ty
                                               __pa(&_stext);
         /* bss */
         g_tboot_shared->mac_regions[2].start = (uint64_t)__pa(&__bss_start);
-        g_tboot_shared->mac_regions[2].size = __pa(&__bss_end) - __pa(&__bss_start);
+#if 0 /* This doesn't work due to -fPIC. */
+        g_tboot_shared->mac_regions[2].size = _sizeof_bss;
+#else
+        asm ( "movl $.sizeof.(.bss),%0"
+              : "=m" (g_tboot_shared->mac_regions[2].size) );
+#endif
 
         /*
          * MAC domains and other Xen memory
--- a/xen/arch/x86/xen.lds.S
+++ b/xen/arch/x86/xen.lds.S
@@ -58,7 +58,6 @@ SECTIONS
   . = __XEN_VIRT_START + MB(1);
   _start = .;
   .text : {
-        _stext = .;            /* Text and read-only data */
        *(.text)
        *(.text.cold)
        *(.text.unlikely)
@@ -77,7 +76,6 @@ SECTIONS
 
   __2M_rodata_start = .;       /* Start of 2M superpages, mapped RO. */
   .rodata : {
-       _srodata = .;
        /* Bug frames table */
        . = ALIGN(4);
        __start_bug_frames = .;
@@ -149,7 +147,6 @@ SECTIONS
   . = ALIGN(PAGE_SIZE);             /* Init code and data */
   __init_begin = .;
   .init.text : {
-       _sinittext = .;
        *(.init.text)
        /*
         * Here are the replacement instructions. The linker sticks them
@@ -230,7 +227,6 @@ SECTIONS
   } :text
 
   .bss : {                     /* BSS */
-       __bss_start = .;
        *(.bss.stack_aligned)
        *(.bss.page_aligned*)
        *(.bss)
@@ -323,5 +319,5 @@ ASSERT(IS_ALIGNED(__init_end,   PAGE_SIZ
 
 ASSERT(IS_ALIGNED(trampoline_start, 4), "trampoline_start misaligned")
 ASSERT(IS_ALIGNED(trampoline_end,   4), "trampoline_end misaligned")
-ASSERT(IS_ALIGNED(__bss_start,      4), "__bss_start misaligned")
-ASSERT(IS_ALIGNED(__bss_end,        4), "__bss_end misaligned")
+ASSERT(IS_ALIGNED(.startof..bss,    4), ".bss misaligned")
+ASSERT(IS_ALIGNED(.sizeof..bss,     4), ".bss size misaligned")
--- a/xen/include/xen/kernel.h
+++ b/xen/include/xen/kernel.h
@@ -71,24 +71,34 @@ extern char _start[], _end[], start[];
     (__p >= _start) && (__p < _end);            \
 })
 
-extern char _stext[], _etext[];
+extern const char _stext[] asm(".startof.(.text)");
+extern const char _etext[];
 #define is_kernel_text(p) ({                    \
     char *__p = (char *)(unsigned long)(p);     \
     (__p >= _stext) && (__p < _etext);          \
 })
 
-extern const char _srodata[], _erodata[];
+extern const char _sizeof_text[] asm(".sizeof.(.text)");
+#define _sizeof_text ((unsigned long)_sizeof_text)
+
+extern const char _srodata[] asm(".startof.(.rodata)");
+extern const char _erodata[];
 #define is_kernel_rodata(p) ({                  \
     const char *__p = (const char *)(unsigned long)(p);     \
     (__p >= _srodata) && (__p < _erodata);      \
 })
 
-extern char _sinittext[], _einittext[];
+extern const char _sinittext[] asm(".startof.(.init.text)");
+extern const char _einittext[];
 #define is_kernel_inittext(p) ({                \
     char *__p = (char *)(unsigned long)(p);     \
     (__p >= _sinittext) && (__p < _einittext);  \
 })
 
+extern char __bss_start[] asm(".startof.(.bss)");
+extern const char _sizeof_bss[] asm(".sizeof.(.bss)");
+#define _sizeof_bss ((unsigned long)_sizeof_bss)
+
 extern enum system_state {
     SYS_STATE_early_boot,
     SYS_STATE_boot,
--- a/xen/tools/symbols.c
+++ b/xen/tools/symbols.c
@@ -143,11 +143,12 @@ static int read_symbol(FILE *in, struct
 		sym++;
 
 	/* Ignore most absolute/undefined (?) symbols. */
-	if (strcmp(sym, "_stext") == 0)
+	if (strcmp(sym, "_stext") == 0 || strcmp(sym, ".startof..text") == 0)
 		_stext = s->addr;
 	else if (strcmp(sym, "_etext") == 0)
 		_etext = s->addr;
-	else if (strcmp(sym, "_sinittext") == 0)
+	else if (strcmp(sym, "_sinittext") == 0 ||
+		 strcmp(sym, ".startof..init.text") == 0)
 		_sinittext = s->addr;
 	else if (strcmp(sym, "_einittext") == 0)
 		_einittext = s->addr;
@@ -168,6 +169,9 @@ static int read_symbol(FILE *in, struct
 	/* exclude also MIPS ELF local symbols ($L123 instead of .L123) */
 	else if (str[0] == '$')
 		goto skip_tail;
+	/* Also strip .startof. symbols. */
+	if (strncmp(sym, ".startof.", 9) == 0)
+		goto skip_tail;
 
 	/* include the type field in the symbol name, so that it gets
 	 * compressed together */

[-- Attachment #3: Type: text/plain, Size: 127 bytes --]

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Re: [PATCH 1/2] x86: force suitable alignment in sources rather than in linker script

[Andrew Cooper]

On 12/08/16 15:47, Jan Beulich wrote:
> Besides being more logical this also allows verifying correct recording
> of alignments in .o files.
>
> The cpu0_stack related ASSERT() in xen.lds.S is now of questionable
> value (as it now verifies correct tool chain behavior), but I've left
> it in nevertheless.
>
> Signed-off-by: Jan Beulich <jbeulich@suse.com>
>
> --- a/xen/arch/x86/hvm/hvm.c
> +++ b/xen/arch/x86/hvm/hvm.c
> @@ -89,6 +89,7 @@ struct hvm_function_table hvm_funcs __re
>   */
>  #define HVM_IOBITMAP_SIZE (3 * PAGE_SIZE)
>  unsigned long __section(".bss.page_aligned")
> +    __attribute__((aligned(PAGE_SIZE)))

Can I talk you into introducing #define __aligned(x)
__attribute__((aligned(x))) in compiler.h ?

Otherwise, Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>

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Re: [PATCH 1/2] x86: force suitable alignment in sources rather than in linker script

[Jan Beulich]

>>> On 12.08.16 at 17:02, <andrew.cooper3@citrix.com> wrote:
> On 12/08/16 15:47, Jan Beulich wrote:
>> Besides being more logical this also allows verifying correct recording
>> of alignments in .o files.
>>
>> The cpu0_stack related ASSERT() in xen.lds.S is now of questionable
>> value (as it now verifies correct tool chain behavior), but I've left
>> it in nevertheless.
>>
>> Signed-off-by: Jan Beulich <jbeulich@suse.com>
>>
>> --- a/xen/arch/x86/hvm/hvm.c
>> +++ b/xen/arch/x86/hvm/hvm.c
>> @@ -89,6 +89,7 @@ struct hvm_function_table hvm_funcs __re
>>   */
>>  #define HVM_IOBITMAP_SIZE (3 * PAGE_SIZE)
>>  unsigned long __section(".bss.page_aligned")
>> +    __attribute__((aligned(PAGE_SIZE)))
> 
> Can I talk you into introducing #define __aligned(x)
> __attribute__((aligned(x))) in compiler.h ?

Sure, I was on the edge of introducing it while putting this together
anyway, but then thought it's maybe not worth it.

> Otherwise, Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>

Thanks, Jan


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Re: [PATCH 1/2] x86: force suitable alignment in sources rather than in linker script

[Andrew Cooper]

On 12/08/16 16:21, Jan Beulich wrote:
>>>> On 12.08.16 at 17:02, <andrew.cooper3@citrix.com> wrote:
>> On 12/08/16 15:47, Jan Beulich wrote:
>>> Besides being more logical this also allows verifying correct recording
>>> of alignments in .o files.
>>>
>>> The cpu0_stack related ASSERT() in xen.lds.S is now of questionable
>>> value (as it now verifies correct tool chain behavior), but I've left
>>> it in nevertheless.
>>>
>>> Signed-off-by: Jan Beulich <jbeulich@suse.com>
>>>
>>> --- a/xen/arch/x86/hvm/hvm.c
>>> +++ b/xen/arch/x86/hvm/hvm.c
>>> @@ -89,6 +89,7 @@ struct hvm_function_table hvm_funcs __re
>>>   */
>>>  #define HVM_IOBITMAP_SIZE (3 * PAGE_SIZE)
>>>  unsigned long __section(".bss.page_aligned")
>>> +    __attribute__((aligned(PAGE_SIZE)))
>> Can I talk you into introducing #define __aligned(x)
>> __attribute__((aligned(x))) in compiler.h ?
> Sure, I was on the edge of introducing it while putting this together
> anyway, but then thought it's maybe not worth it.

I have been meaning to do it for a while, and clean up the existing
opencoded uses in the tree.

~Andrew

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Re: [PATCH 2/2] make use of .startof.() and .sizeof.() assembler expressions

[Andrew Cooper]

On 12/08/16 15:48, Jan Beulich wrote:
> Section start symbols frequently obscure the actual symbol name living
> at the start of the section. Eliminate them where they can be replaced
> by linker resolved .startof.* symbols. (Section end symbols may have
> the same undesirable effect, but they're less easy to eliminate, as
> they'd need to be represented by the sum of .startof.<section> and
> .sizeof.<section>).
>
> Along those lines use .sizeof.* where section sizes get calculated
> from the difference of section and and section start symbols.
>
> Note that this would be nice for the build-id section too, but:
> - The generated (by ld) section names differ between ELF and COFF/PE
>   (ELF: .note.gnu.build-id; COFF/PE[2.26+]: .buildid), yet we compile
>   version.c just once (and hence can use only either of the necessary
>   .startof./.sizeof. forms).
> - The ELF section name needs to be quoted in the .startof./.sizeof.
>   expressions, yet that quoting is supported only by gas 2.26+.
>
> Signed-off-by: Jan Beulich <jbeulich@suse.com>

Is there any documentation of these?  I cant seem to find any.

Does this work on Clang at all?

~Andrew

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Re: [PATCH 2/2] make use of .startof.() and .sizeof.() assembler expressions

[Jan Beulich]

>>> On 15.08.16 at 11:43, <andrew.cooper3@citrix.com> wrote:
> On 12/08/16 15:48, Jan Beulich wrote:
>> Section start symbols frequently obscure the actual symbol name living
>> at the start of the section. Eliminate them where they can be replaced
>> by linker resolved .startof.* symbols. (Section end symbols may have
>> the same undesirable effect, but they're less easy to eliminate, as
>> they'd need to be represented by the sum of .startof.<section> and
>> .sizeof.<section>).
>>
>> Along those lines use .sizeof.* where section sizes get calculated
>> from the difference of section and and section start symbols.
>>
>> Note that this would be nice for the build-id section too, but:
>> - The generated (by ld) section names differ between ELF and COFF/PE
>>   (ELF: .note.gnu.build-id; COFF/PE[2.26+]: .buildid), yet we compile
>>   version.c just once (and hence can use only either of the necessary
>>   .startof./.sizeof. forms).
>> - The ELF section name needs to be quoted in the .startof./.sizeof.
>>   expressions, yet that quoting is supported only by gas 2.26+.
>>
>> Signed-off-by: Jan Beulich <jbeulich@suse.com>
> 
> Is there any documentation of these?  I cant seem to find any.

Indeed I can't find any either, at least not inside the binutils
repo. But the support for this has been there for a long time
(it is present in 2.16.1, which is the oldest I have readily available).

> Does this work on Clang at all?

To be honest - I have no idea.

Jan


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