[PATCH v2 12/14] xen/riscv: introduce an implementation of macros from <asm/bug.h>

[Oleksii Kurochko <oleksii.kurochko@gmail.com>]

The patch introduces macros: BUG(), WARN(), run_in_exception(),
assert_failed.

The implementation uses "ebreak" instruction in combination with
diffrent bug frame tables (for each type) which contains useful
information.

Signed-off-by: Oleksii Kurochko <oleksii.kurochko@gmail.com>
---
Changes:
  - Remove __ in define namings
  - Update run_in_exception_handler() with
    register void *fn_ asm(__stringify(BUG_FN_REG)) = (fn);
  - Remove bug_instr_t type and change it's usage to uint32_t
---
 xen/arch/riscv/include/asm/bug.h | 118 ++++++++++++++++++++++++++++
 xen/arch/riscv/traps.c           | 128 +++++++++++++++++++++++++++++++
 xen/arch/riscv/xen.lds.S         |  10 +++
 3 files changed, 256 insertions(+)
 create mode 100644 xen/arch/riscv/include/asm/bug.h

diff --git a/xen/arch/riscv/include/asm/bug.h b/xen/arch/riscv/include/asm/bug.h
new file mode 100644
index 0000000000..4b15d8eba6
--- /dev/null
+++ b/xen/arch/riscv/include/asm/bug.h
@@ -0,0 +1,118 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2012 Regents of the University of California
+ * Copyright (C) 2021-2023 Vates
+ *
+ */
+
+#ifndef _ASM_RISCV_BUG_H
+#define _ASM_RISCV_BUG_H
+
+#include <xen/stringify.h>
+#include <xen/types.h>
+
+#ifndef __ASSEMBLY__
+
+struct bug_frame {
+    signed int loc_disp;    /* Relative address to the bug address */
+    signed int file_disp;   /* Relative address to the filename */
+    signed int msg_disp;    /* Relative address to the predicate (for ASSERT) */
+    uint16_t line;          /* Line number */
+    uint32_t pad0:16;       /* Padding for 8-bytes align */
+};
+
+#define bug_loc(b) ((const void *)(b) + (b)->loc_disp)
+#define bug_file(b) ((const void *)(b) + (b)->file_disp);
+#define bug_line(b) ((b)->line)
+#define bug_msg(b) ((const char *)(b) + (b)->msg_disp)
+
+#define BUGFRAME_run_fn 0
+#define BUGFRAME_warn   1
+#define BUGFRAME_bug    2
+#define BUGFRAME_assert 3
+
+#define BUGFRAME_NR     4
+
+#define INSN_LENGTH_MASK        _UL(0x3)
+#define INSN_LENGTH_32          _UL(0x3)
+
+#define BUG_INSN_32             _UL(0x00100073) /* ebreak */
+#define BUG_INSN_16             _UL(0x9002) /* c.ebreak */
+#define COMPRESSED_INSN_MASK    _UL(0xffff)
+
+#define GET_INSN_LENGTH(insn)                               \
+({                                                          \
+    unsigned long len;                                      \
+    len = ((insn & INSN_LENGTH_MASK) == INSN_LENGTH_32) ?   \
+        4UL : 2UL;                                          \
+    len;                                                    \
+})
+
+/* These are defined by the architecture */
+int is_valid_bugaddr(uint32_t addr);
+
+#define BUG_FN_REG t0
+
+/* Many versions of GCC doesn't support the asm %c parameter which would
+ * be preferable to this unpleasantness. We use mergeable string
+ * sections to avoid multiple copies of the string appearing in the
+ * Xen image. BUGFRAME_run_fn needs to be handled separately.
+ */
+#define BUG_FRAME(type, line, file, has_msg, msg) do {                      \
+    asm ("1:ebreak\n"                                                       \
+         ".pushsection .rodata.str, \"aMS\", %progbits, 1\n"                \
+         "2:\t.asciz " __stringify(file) "\n"                               \
+         "3:\n"                                                             \
+         ".if " #has_msg "\n"                                               \
+         "\t.asciz " #msg "\n"                                              \
+         ".endif\n"                                                         \
+         ".popsection\n"                                                    \
+         ".pushsection .bug_frames." __stringify(type) ", \"a\", %progbits\n"\
+         "4:\n"                                                             \
+         ".p2align 2\n"                                                     \
+         ".long (1b - 4b)\n"                                                \
+         ".long (2b - 4b)\n"                                                \
+         ".long (3b - 4b)\n"                                                \
+         ".hword " __stringify(line) ", 0\n"                                \
+         ".popsection");                                                    \
+} while (0)
+
+/*
+ * GCC will not allow to use "i"  when PIE is enabled (Xen doesn't set the
+ * flag but instead rely on the default value from the compiler). So the
+ * easiest way to implement run_in_exception_handler() is to pass the to
+ * be called function in a fixed register.
+ */
+#define  run_in_exception_handler(fn) do {                                  \
+    register void *fn_ asm(__stringify(BUG_FN_REG)) = (fn);                 \
+    asm ("1:ebreak\n"                                                       \
+         ".pushsection .bug_frames." __stringify(BUGFRAME_run_fn) ","       \
+         "             \"a\", %%progbits\n"                                 \
+         "2:\n"                                                             \
+         ".p2align 2\n"                                                     \
+         ".long (1b - 2b)\n"                                                \
+         ".long 0, 0, 0\n"                                                  \
+         ".popsection" :: "r" (fn_) );                                      \
+} while (0)
+
+#define WARN() BUG_FRAME(BUGFRAME_warn, __LINE__, __FILE__, 0, "")
+
+#define BUG() do {                                              \
+    BUG_FRAME(BUGFRAME_bug,  __LINE__, __FILE__, 0, "");        \
+    unreachable();                                              \
+} while (0)
+
+#define assert_failed(msg) do {                                 \
+    BUG_FRAME(BUGFRAME_assert, __LINE__, __FILE__, 1, msg);     \
+    unreachable();                                              \
+} while (0)
+
+extern const struct bug_frame __start_bug_frames[],
+                              __stop_bug_frames_0[],
+                              __stop_bug_frames_1[],
+                              __stop_bug_frames_2[],
+                              __stop_bug_frames_3[];
+
+#endif /* !__ASSEMBLY__ */
+
+#endif /* _ASM_RISCV_BUG_H */
diff --git a/xen/arch/riscv/traps.c b/xen/arch/riscv/traps.c
index 31ed63e3c1..0afb8e4e42 100644
--- a/xen/arch/riscv/traps.c
+++ b/xen/arch/riscv/traps.c
@@ -4,6 +4,7 @@
  *
  * RISC-V Trap handlers
  */
+#include <asm/bug.h>
 #include <asm/csr.h>
 #include <asm/early_printk.h>
 #include <asm/processor.h>
@@ -97,7 +98,134 @@ static void do_unexpected_trap(const struct cpu_user_regs *regs)
     die();
 }
 
+void show_execution_state(const struct cpu_user_regs *regs)
+{
+    early_printk("implement show_execution_state(regs)\n");
+}
+
+int do_bug_frame(struct cpu_user_regs *regs, vaddr_t pc)
+{
+    struct bug_frame *start, *end;
+    struct bug_frame *bug = NULL;
+    unsigned int id = 0;
+    const char *filename, *predicate;
+    int lineno;
+
+    unsigned long bug_frames[] = {
+        (unsigned long)&__start_bug_frames[0],
+        (unsigned long)&__stop_bug_frames_0[0],
+        (unsigned long)&__stop_bug_frames_1[0],
+        (unsigned long)&__stop_bug_frames_2[0],
+        (unsigned long)&__stop_bug_frames_3[0],
+    };
+
+    for ( id = 0; id < BUGFRAME_NR; id++ )
+    {
+        start = (struct  bug_frame *)bug_frames[id];
+        end = (struct  bug_frame *)bug_frames[id + 1];
+
+        while ( start != end )
+        {
+            if ( (vaddr_t)bug_loc(start) == pc )
+            {
+                bug = start;
+                goto found;
+            }
+
+            start++;
+        }
+    }
+
+ found:
+    if ( bug == NULL )
+        return -ENOENT;
+
+    if ( id == BUGFRAME_run_fn )
+    {
+        void (*fn)(const struct cpu_user_regs *) = (void *)regs->BUG_FN_REG;
+
+        fn(regs);
+
+        goto end;
+    }
+
+    /* WARN, BUG or ASSERT: decode the filename pointer and line number. */
+    filename = bug_file(bug);
+    lineno = bug_line(bug);
+
+    switch ( id )
+    {
+    case BUGFRAME_warn:
+        /*
+         * TODO: change early_printk's function to early_printk with format
+         *       when s(n)printf() will be added.
+         */
+        early_printk("Xen WARN at ");
+        early_printk(filename);
+        early_printk(":");
+        // early_printk_hnum(lineno);
+
+        show_execution_state(regs);
+
+        goto end;
+
+    case BUGFRAME_bug:
+         /*
+          * TODO: change early_printk's function to early_printk with format
+          *       when s(n)printf() will be added.
+          */
+        early_printk("Xen BUG at ");
+        early_printk(filename);
+        early_printk(":");
+        // early_printk_hnum(lineno);
+
+        show_execution_state(regs);
+        early_printk("change wait_for_interrupt to panic() when common is available\n");
+        die();
+
+    case BUGFRAME_assert:
+        /* ASSERT: decode the predicate string pointer. */
+        predicate = bug_msg(bug);
+
+        /*
+         * TODO: change early_printk's function to early_printk with format
+         *       when s(n)printf() will be added.
+         */
+        early_printk("Assertion \'");
+        early_printk(predicate);
+        early_printk("\' failed at ");
+        early_printk(filename);
+        early_printk(":");
+        // early_printk_hnum(lineno);
+
+        show_execution_state(regs);
+        early_printk("change wait_for_interrupt to panic() when common is available\n");
+        die();
+    }
+
+    return -EINVAL;
+
+ end:
+    regs->sepc += GET_INSN_LENGTH(*(uint32_t *)pc);
+
+    return 0;
+}
+
+int is_valid_bugaddr(uint32_t insn)
+{
+    if ((insn & INSN_LENGTH_MASK) == INSN_LENGTH_32)
+        return (insn == BUG_INSN_32);
+    else
+        return ((insn & COMPRESSED_INSN_MASK) == BUG_INSN_16);
+}
+
 void do_trap(struct cpu_user_regs *cpu_regs)
 {
+    register_t pc = cpu_regs->sepc;
+    uint32_t instr = *(uint32_t *)pc;
+
+    if (is_valid_bugaddr(instr))
+        if (!do_bug_frame(cpu_regs, pc)) return;
+
     do_unexpected_trap(cpu_regs);
 }
diff --git a/xen/arch/riscv/xen.lds.S b/xen/arch/riscv/xen.lds.S
index ca57cce75c..139e2d04cb 100644
--- a/xen/arch/riscv/xen.lds.S
+++ b/xen/arch/riscv/xen.lds.S
@@ -39,6 +39,16 @@ SECTIONS
     . = ALIGN(PAGE_SIZE);
     .rodata : {
         _srodata = .;          /* Read-only data */
+        /* Bug frames table */
+       __start_bug_frames = .;
+       *(.bug_frames.0)
+       __stop_bug_frames_0 = .;
+       *(.bug_frames.1)
+       __stop_bug_frames_1 = .;
+       *(.bug_frames.2)
+       __stop_bug_frames_2 = .;
+       *(.bug_frames.3)
+       __stop_bug_frames_3 = .;
         *(.rodata)
         *(.rodata.*)
         *(.data.rel.ro)
-- 
2.39.0