[PATCH 0/2][XTF] build: suppress GNU ld 2.39 warnings

[PATCH 0/2][XTF] build: suppress GNU ld 2.39 warnings

[Jan Beulich]

Like done previously for the hypervisor and elsewhere.

1: suppress GNU ld 2.39 warning about RWX load segments
2: silence GNU ld 2.39 warning about executable stacks

Jan

[PATCH 1/2][XTF] build: suppress GNU ld 2.39 warning about RWX load segments

[Jan Beulich]

We cannot really avoid such and we're also not really at risk because of
them, as we control page table permissions ourselves rather than relying
on a loader of some sort.

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

--- a/build/common.mk
+++ b/build/common.mk
@@ -20,9 +20,15 @@ COMMON_FLAGS := -pipe -I$(ROOT)/include
 cc-option = $(shell if [ -z "`echo 'int p=1;' | $(CC) $(1) -S -o /dev/null -x c - 2>&1`" ]; \
 			then echo y; else echo n; fi)
 
+ld-option = $(shell if $(LD) -v $(1) >/dev/null 2>&1; then echo y; else echo n; fi)
+
 # Disable PIE, but need to check if compiler supports it
 COMMON_CFLAGS-$(call cc-option,-no-pie) += -no-pie
 
+# Suppress warnings about LOAD segments with RWX permissions, as what we build
+# aren't normal user-mode executables.
+LDFLAGS-$(call ld-option,--warn-rwx-segments) := --no-warn-rwx-segments
+
 COMMON_AFLAGS := $(COMMON_FLAGS) -D__ASSEMBLY__
 COMMON_CFLAGS := $(COMMON_FLAGS) $(COMMON_CFLAGS-y)
 COMMON_CFLAGS += -Wall -Wextra -Werror -std=gnu99 -Wstrict-prototypes -O3 -g

[PATCH 2/2][XTF] build: silence GNU ld 2.39 warning about executable stacks

[Jan Beulich]

While for C files the compiler is supposed to arrange for emitting
respective information, for assembly sources we're responsible ourselves.

For the new use of cc-option to work we cannot pass -S to the compiler
anymore. We need the compiler to actually invoke the assembler, so switch
to using -c.

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

--- a/build/common.mk
+++ b/build/common.mk
@@ -15,9 +15,11 @@ $(foreach env,$(HVM_ENVIRONMENTS),$(eval
 $(foreach env,$(32BIT_ENVIRONMENTS),$(eval $(env)_arch := x86_32))
 $(foreach env,$(64BIT_ENVIRONMENTS),$(eval $(env)_arch := x86_64))
 
+comma := ,
+
 COMMON_FLAGS := -pipe -I$(ROOT)/include -I$(ROOT)/arch/x86/include -MMD -MP
 
-cc-option = $(shell if [ -z "`echo 'int p=1;' | $(CC) $(1) -S -o /dev/null -x c - 2>&1`" ]; \
+cc-option = $(shell if [ -z "`echo 'int p=1;' | $(CC) $(1) -c -o /dev/null -x c - 2>&1`" ]; \
 			then echo y; else echo n; fi)
 
 ld-option = $(shell if $(LD) -v $(1) >/dev/null 2>&1; then echo y; else echo n; fi)
@@ -25,11 +27,15 @@ ld-option = $(shell if $(LD) -v $(1) >/d
 # Disable PIE, but need to check if compiler supports it
 COMMON_CFLAGS-$(call cc-option,-no-pie) += -no-pie
 
+# Arrange for assembly files to have a proper .note.GNU-stack section added,
+# to silence warnings otherwise issued by GNU ld 2.39 and newer.
+COMMON_AFLAGS-$(call cc-option,-Wa$(comma)--noexecstack) += -Wa,--noexecstack
+
 # Suppress warnings about LOAD segments with RWX permissions, as what we build
 # aren't normal user-mode executables.
 LDFLAGS-$(call ld-option,--warn-rwx-segments) := --no-warn-rwx-segments
 
-COMMON_AFLAGS := $(COMMON_FLAGS) -D__ASSEMBLY__
+COMMON_AFLAGS := $(COMMON_FLAGS) -D__ASSEMBLY__ $(COMMON_AFLAGS-y)
 COMMON_CFLAGS := $(COMMON_FLAGS) $(COMMON_CFLAGS-y)
 COMMON_CFLAGS += -Wall -Wextra -Werror -std=gnu99 -Wstrict-prototypes -O3 -g
 COMMON_CFLAGS += -fno-common -fno-asynchronous-unwind-tables -fno-strict-aliasing

Re: [PATCH 0/2][XTF] build: suppress GNU ld 2.39 warnings

[Andrew Cooper]

On 29/09/2022 11:03, Jan Beulich wrote:
> Like done previously for the hypervisor and elsewhere.
>
> 1: suppress GNU ld 2.39 warning about RWX load segments
> 2: silence GNU ld 2.39 warning about executable stacks

I've taken these, and dropped the `-no-pie`, but there's something else too.

$readelf -Wa tests/example/test-hvm64-example
...

No version information found in this file.

Displaying notes found in: .note
  Owner                Data size     Description
  GNU                  0x00000020    NT_GNU_PROPERTY_TYPE_0         
Properties: x86 feature used: x86, <corrupt type (0) datasz: 0xc0010002>

readelf: Warning: note with invalid namesz and/or descsz found at offset
0x30
readelf: Warning:  type: 0x12, namesize: 0x00000004, descsize:
0x00000004, alignment: 8


It's only hvm64 which reads as corrupt, so I think there's some
collateral damage with the conversion between ELF64 and ELF32.

~Andrew

Re: [PATCH 0/2][XTF] build: suppress GNU ld 2.39 warnings

[Jan Beulich]

On 03.10.2022 15:44, Andrew Cooper wrote:
> On 29/09/2022 11:03, Jan Beulich wrote:
>> Like done previously for the hypervisor and elsewhere.
>>
>> 1: suppress GNU ld 2.39 warning about RWX load segments
>> 2: silence GNU ld 2.39 warning about executable stacks
> 
> I've taken these, and dropped the `-no-pie`, but there's something else too.
> 
> $readelf -Wa tests/example/test-hvm64-example
> ...
> 
> No version information found in this file.
> 
> Displaying notes found in: .note
>   Owner                Data size     Description
>   GNU                  0x00000020    NT_GNU_PROPERTY_TYPE_0         
> Properties: x86 feature used: x86, <corrupt type (0) datasz: 0xc0010002>
> 
> readelf: Warning: note with invalid namesz and/or descsz found at offset
> 0x30
> readelf: Warning:  type: 0x12, namesize: 0x00000004, descsize:
> 0x00000004, alignment: 8
> 
> 
> It's only hvm64 which reads as corrupt, so I think there's some
> collateral damage with the conversion between ELF64 and ELF32.

Iirc there was a binary-incompatible change (accompanying an
incompatible change to the ELF spec) to how notes are generated /
processed for 64-bit objects (some hand waving involved here, as
this did happen quite a while back). I assume the .note section(s)
will need converting (to insert / remove padding) in the course of
converting between ELF32 and ELF64.

Jan