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[PATCH] tcg: Use the GDB JIT debugging interface.
- From: Richard Henderson <rth at twiddle dot net>
- To: libc-alpha at sourceware dot org
- Cc: peter dot maydell at linaro dot org
- Date: Tue, 20 Mar 2012 10:53:18 -0700
- Subject: [PATCH] tcg: Use the GDB JIT debugging interface.
- References: <1332265998-22023-1-git-send-email-rth@twiddle.net>
This allows us to generate unwind info for the dynamicly generated
code in the code_gen_buffer. Only i386 is converted at this point.
Signed-off-by: Richard Henderson <rth@twiddle.net>
---
elf.h | 1 +
exec.c | 1 +
tcg/i386/tcg-target.c | 114 +++++++++++++++++++--
tcg/tcg.c | 277 +++++++++++++++++++++++++++++++++++++++++++++++++
tcg/tcg.h | 2 +
5 files changed, 386 insertions(+), 9 deletions(-)
diff --git a/elf.h b/elf.h
index 2e05d34..310e05a 100644
--- a/elf.h
+++ b/elf.h
@@ -216,6 +216,7 @@ typedef int64_t Elf64_Sxword;
#define ELF_ST_BIND(x) ((x) >> 4)
#define ELF_ST_TYPE(x) (((unsigned int) x) & 0xf)
+#define ELF_ST_INFO(bind, type) (((bind) << 4) | ((type) & 0xf))
#define ELF32_ST_BIND(x) ELF_ST_BIND(x)
#define ELF32_ST_TYPE(x) ELF_ST_TYPE(x)
#define ELF64_ST_BIND(x) ELF_ST_BIND(x)
diff --git a/exec.c b/exec.c
index be392e2..dd24939 100644
--- a/exec.c
+++ b/exec.c
@@ -636,6 +636,7 @@ void tcg_exec_init(unsigned long tb_size)
cpu_gen_init();
code_gen_alloc(tb_size);
code_gen_ptr = code_gen_buffer;
+ tcg_register_jit(code_gen_buffer, code_gen_buffer_size);
page_init();
#if !defined(CONFIG_USER_ONLY) || !defined(CONFIG_USE_GUEST_BASE)
/* There's no guest base to take into account, so go ahead and
diff --git a/tcg/i386/tcg-target.c b/tcg/i386/tcg-target.c
index 43a51a1..871a7e7 100644
--- a/tcg/i386/tcg-target.c
+++ b/tcg/i386/tcg-target.c
@@ -1989,22 +1989,29 @@ static int tcg_target_callee_save_regs[] = {
#endif
};
+/* Compute frame size via macros, to share between tcg_target_qemu_prologue
+ and tcg_register_jit. */
+
+#define PUSH_SIZE \
+ ((1 + ARRAY_SIZE(tcg_target_callee_save_regs)) \
+ * (TCG_TARGET_REG_BITS / 8))
+
+#define FRAME_SIZE \
+ ((PUSH_SIZE \
+ + TCG_STATIC_CALL_ARGS_SIZE \
+ + CPU_TEMP_BUF_NLONGS * sizeof(long) \
+ + TCG_TARGET_STACK_ALIGN - 1) \
+ & ~(TCG_TARGET_STACK_ALIGN - 1))
+
/* Generate global QEMU prologue and epilogue code */
static void tcg_target_qemu_prologue(TCGContext *s)
{
- int i, frame_size, push_size, stack_addend;
+ int i, stack_addend;
/* TB prologue */
/* Reserve some stack space, also for TCG temps. */
- push_size = 1 + ARRAY_SIZE(tcg_target_callee_save_regs);
- push_size *= TCG_TARGET_REG_BITS / 8;
-
- frame_size = push_size + TCG_STATIC_CALL_ARGS_SIZE +
- CPU_TEMP_BUF_NLONGS * sizeof(long);
- frame_size = (frame_size + TCG_TARGET_STACK_ALIGN - 1) &
- ~(TCG_TARGET_STACK_ALIGN - 1);
- stack_addend = frame_size - push_size;
+ stack_addend = FRAME_SIZE - PUSH_SIZE;
tcg_set_frame(s, TCG_REG_CALL_STACK, TCG_STATIC_CALL_ARGS_SIZE,
CPU_TEMP_BUF_NLONGS * sizeof(long));
@@ -2070,3 +2077,92 @@ static void tcg_target_init(TCGContext *s)
tcg_add_target_add_op_defs(x86_op_defs);
}
+
+typedef struct {
+ uint32_t len __attribute__((aligned((sizeof(void *)))));
+ uint32_t id;
+ uint8_t version;
+ char augmentation[1];
+ uint8_t code_align;
+ uint8_t data_align;
+ uint8_t return_column;
+} DebugFrameCIE;
+
+typedef struct {
+ uint32_t len __attribute__((aligned((sizeof(void *)))));
+ uint32_t cie_offset;
+ tcg_target_long func_start __attribute__((packed));
+ tcg_target_long func_len __attribute__((packed));
+ uint8_t def_cfa[4];
+ uint8_t reg_ofs[14];
+} DebugFrameFDE;
+
+typedef struct {
+ DebugFrameCIE cie;
+ DebugFrameFDE fde;
+} DebugFrame;
+
+#if TCG_TARGET_REG_BITS == 64
+#define ELF_HOST_MACHINE EM_X86_64
+static DebugFrame debug_frame = {
+ .cie.len = sizeof(DebugFrameCIE)-4, /* length after .len member */
+ .cie.id = -1,
+ .cie.version = 1,
+ .cie.code_align = 1,
+ .cie.data_align = 0x78, /* sleb128 -8 */
+ .cie.return_column = 16,
+
+ .fde.len = sizeof(DebugFrameFDE)-4, /* length after .len member */
+ .fde.def_cfa = {
+ 12, 7, /* DW_CFA_def_cfa %rsp, ... */
+ (FRAME_SIZE & 0x7f) | 0x80, /* ... uleb128 FRAME_SIZE */
+ (FRAME_SIZE >> 7)
+ },
+ .fde.reg_ofs = {
+ 0x90, 1, /* DW_CFA_offset, %rip, -8 */
+ /* The following ordering must match tcg_target_callee_save_regs. */
+ 0x86, 2, /* DW_CFA_offset, %rbp, -16 */
+ 0x83, 3, /* DW_CFA_offset, %rbx, -24 */
+ 0x8c, 4, /* DW_CFA_offset, %r12, -32 */
+ 0x8d, 5, /* DW_CFA_offset, %r13, -40 */
+ 0x8e, 6, /* DW_CFA_offset, %r14, -48 */
+ 0x8f, 7, /* DW_CFA_offset, %r15, -56 */
+ }
+};
+#else
+#define ELF_HOST_MACHINE EM_386
+static DebugFrame debug_frame = {
+ .cie.len = sizeof(DebugFrameCIE)-4, /* length after .len member */
+ .cie.id = -1,
+ .cie.version = 1,
+ .cie.code_align = 1,
+ .cie.data_align = 0x7c, /* sleb128 -4 */
+ .cie.return_column = 8,
+
+ .fde.len = sizeof(DebugFrameFDE)-4, /* length after .len member */
+ .fde.def_cfa = {
+ 12, 4, /* DW_CFA_def_cfa %esp, ... */
+ (FRAME_SIZE & 0x7f) | 0x80, /* ... uleb128 FRAME_SIZE */
+ (FRAME_SIZE >> 7)
+ },
+ .fde.reg_ofs = {
+ 0x88, 1, /* DW_CFA_offset, %eip, -4 */
+ /* The following ordering must match tcg_target_callee_save_regs. */
+ 0x85, 2, /* DW_CFA_offset, %ebp, -8 */
+ 0x83, 3, /* DW_CFA_offset, %ebx, -12 */
+ 0x86, 4, /* DW_CFA_offset, %esi, -16 */
+ 0x87, 5, /* DW_CFA_offset, %edi, -20 */
+ }
+};
+#endif
+
+void tcg_register_jit(void *buf, size_t buf_size)
+{
+ /* We're expecting a 2 byte uleb128 encoded value. */
+ assert(FRAME_SIZE >> 14 == 0);
+
+ debug_frame.fde.func_start = (tcg_target_long) buf;
+ debug_frame.fde.func_len = buf_size;
+
+ tcg_register_jit_int(buf, buf_size, &debug_frame, sizeof(debug_frame));
+}
diff --git a/tcg/tcg.c b/tcg/tcg.c
index ccfcd1a..df4edc0 100644
--- a/tcg/tcg.c
+++ b/tcg/tcg.c
@@ -28,6 +28,9 @@
#include "config.h"
+/* Define to jump the ELF file used to communicate with GDB. */
+#undef DEBUG_JIT
+
#if !defined(CONFIG_DEBUG_TCG) && !defined(NDEBUG)
/* define it to suppress various consistency checks (faster) */
#define NDEBUG
@@ -45,6 +48,18 @@
#include "cpu.h"
#include "tcg-op.h"
+
+#if TCG_TARGET_REG_BITS == 64
+# define ELF_CLASS ELFCLASS64
+#else
+# define ELF_CLASS ELFCLASS32
+#endif
+#ifdef HOST_WORDS_BIGENDIAN
+# define ELF_DATA ELFDATA2MSB
+#else
+# define ELF_DATA ELFDATA2LSB
+#endif
+
#include "elf.h"
#if defined(CONFIG_USE_GUEST_BASE) && !defined(TCG_TARGET_HAS_GUEST_BASE)
@@ -57,6 +72,10 @@ static void tcg_target_qemu_prologue(TCGContext *s);
static void patch_reloc(uint8_t *code_ptr, int type,
tcg_target_long value, tcg_target_long addend);
+static void tcg_register_jit_int(void *buf, size_t size,
+ void *debug_frame, size_t debug_frame_size)
+ __attribute__((unused));
+
/* Forward declarations for functions declared and used in tcg-target.c. */
static int target_parse_constraint(TCGArgConstraint *ct, const char **pct_str);
static void tcg_out_ld(TCGContext *s, TCGType type, TCGReg ret, TCGReg arg1,
@@ -2231,3 +2250,261 @@ void tcg_dump_info(FILE *f, fprintf_function cpu_fprintf)
cpu_fprintf(f, "[TCG profiler not compiled]\n");
}
#endif
+
+#ifdef ELF_HOST_MACHINE
+/* In order to use this feature, the backend needs to do three things:
+
+ (1) Define ELF_HOST_MACHINE to indicate both what value to
+ put into the ELF image and to indicate support for the feature.
+
+ (2) Define tcg_register_jit. This should create a buffer containing
+ the contents of a .debug_frame section that describes the post-
+ prologue unwind info for the tcg machine.
+
+ (3) Call tcg_register_jit_int, with the constructed .debug_frame.
+*/
+
+/* Begin GDB interface. THE FOLLOWING MUST MATCH GDB DOCS. */
+typedef enum {
+ JIT_NOACTION = 0,
+ JIT_REGISTER_FN,
+ JIT_UNREGISTER_FN
+} jit_actions_t;
+
+struct jit_code_entry {
+ struct jit_code_entry *next_entry;
+ struct jit_code_entry *prev_entry;
+ const void *symfile_addr;
+ uint64_t symfile_size;
+};
+
+struct jit_descriptor {
+ uint32_t version;
+ uint32_t action_flag;
+ struct jit_code_entry *relevant_entry;
+ struct jit_code_entry *first_entry;
+};
+
+void __jit_debug_register_code(void) __attribute__((noinline));
+void __jit_debug_register_code(void)
+{
+ asm("");
+}
+
+/* Must statically initialize the version, because GDB may check
+ the version before we can set it. */
+struct jit_descriptor __jit_debug_descriptor = { 1, 0, 0, 0 };
+
+/* End GDB interface. */
+
+static int find_string(const char *strtab, const char *str)
+{
+ const char *p = strtab + 1;
+
+ while (1) {
+ if (strcmp(p, str) == 0) {
+ return p - strtab;
+ }
+ p += strlen(p) + 1;
+ }
+}
+
+static void tcg_register_jit_int(void *buf_ptr, size_t buf_size,
+ void *debug_frame, size_t debug_frame_size)
+{
+ struct __attribute__((packed)) DebugInfo {
+ uint32_t len;
+ uint16_t version;
+ uint32_t abbrev;
+ uint8_t ptr_size;
+ uint8_t cu_die;
+ uint16_t cu_lang;
+ uintptr_t cu_low_pc;
+ uintptr_t cu_high_pc;
+ uint8_t fn_die;
+ char fn_name[16];
+ uintptr_t fn_low_pc;
+ uintptr_t fn_high_pc;
+ uint8_t cu_eoc;
+ };
+
+ struct ElfImage {
+ ElfW(Ehdr) ehdr;
+ ElfW(Phdr) phdr;
+ ElfW(Shdr) shdr[7];
+ ElfW(Sym) sym[2];
+ struct DebugInfo di;
+ uint8_t da[24];
+ char str[80];
+ };
+
+ struct ElfImage *img;
+
+ static const struct ElfImage img_template = {
+ .ehdr = {
+ .e_ident[EI_MAG0] = ELFMAG0,
+ .e_ident[EI_MAG1] = ELFMAG1,
+ .e_ident[EI_MAG2] = ELFMAG2,
+ .e_ident[EI_MAG3] = ELFMAG3,
+ .e_ident[EI_CLASS] = ELF_CLASS,
+ .e_ident[EI_DATA] = ELF_DATA,
+ .e_ident[EI_VERSION] = EV_CURRENT,
+ .e_type = ET_EXEC,
+ .e_machine = ELF_HOST_MACHINE,
+ .e_version = EV_CURRENT,
+ .e_phoff = offsetof(struct ElfImage, phdr),
+ .e_shoff = offsetof(struct ElfImage, shdr),
+ .e_ehsize = sizeof(ElfW(Shdr)),
+ .e_phentsize = sizeof(ElfW(Phdr)),
+ .e_phnum = 1,
+ .e_shentsize = sizeof(ElfW(Shdr)),
+ .e_shnum = ARRAY_SIZE(img->shdr),
+ .e_shstrndx = ARRAY_SIZE(img->shdr) - 1,
+ },
+ .phdr = {
+ .p_type = PT_LOAD,
+ .p_flags = PF_X,
+ },
+ .shdr = {
+ [0] = { .sh_type = SHT_NULL },
+ /* Trick: The contents of code_gen_buffer are not present in
+ this fake ELF file; that got allocated elsewhere. Therefore
+ we mark .text as SHT_NOBITS (similar to .bss) so that readers
+ will not look for contents. We can record any address. */
+ [1] = { /* .text */
+ .sh_type = SHT_NOBITS,
+ .sh_flags = SHF_EXECINSTR | SHF_ALLOC,
+ },
+ [2] = { /* .debug_info */
+ .sh_type = SHT_PROGBITS,
+ .sh_offset = offsetof(struct ElfImage, di),
+ .sh_size = sizeof(struct DebugInfo),
+ },
+ [3] = { /* .debug_abbrev */
+ .sh_type = SHT_PROGBITS,
+ .sh_offset = offsetof(struct ElfImage, da),
+ .sh_size = sizeof(img->da),
+ },
+ [4] = { /* .debug_frame */
+ .sh_type = SHT_PROGBITS,
+ .sh_offset = sizeof(struct ElfImage),
+ },
+ [5] = { /* .symtab */
+ .sh_type = SHT_SYMTAB,
+ .sh_offset = offsetof(struct ElfImage, sym),
+ .sh_size = sizeof(img->sym),
+ .sh_info = 1,
+ .sh_link = ARRAY_SIZE(img->shdr) - 1,
+ .sh_entsize = sizeof(ElfW(Sym)),
+ },
+ [6] = { /* .strtab */
+ .sh_type = SHT_STRTAB,
+ .sh_offset = offsetof(struct ElfImage, str),
+ .sh_size = sizeof(img->str),
+ }
+ },
+ .sym = {
+ [1] = { /* code_gen_buffer */
+ .st_info = ELF_ST_INFO(STB_GLOBAL, STT_FUNC),
+ .st_shndx = 1,
+ }
+ },
+ .di = {
+ .len = sizeof(struct DebugInfo) - 4,
+ .version = 2,
+ .ptr_size = sizeof(void *),
+ .cu_die = 1,
+ .cu_lang = 0x8001, /* DW_LANG_Mips_Assembler */
+ .fn_die = 2,
+ .fn_name = "code_gen_buffer"
+ },
+ .da = {
+ 1, /* abbrev number (the cu) */
+ 0x11, 1, /* DW_TAG_compile_unit, has children */
+ 0x13, 0x5, /* DW_AT_language, DW_FORM_data2 */
+ 0x11, 0x1, /* DW_AT_low_pc, DW_FORM_addr */
+ 0x12, 0x1, /* DW_AT_high_pc, DW_FORM_addr */
+ 0, 0, /* end of abbrev */
+ 2, /* abbrev number (the fn) */
+ 0x2e, 0, /* DW_TAG_subprogram, no children */
+ 0x3, 0x8, /* DW_AT_name, DW_FORM_string */
+ 0x11, 0x1, /* DW_AT_low_pc, DW_FORM_addr */
+ 0x12, 0x1, /* DW_AT_high_pc, DW_FORM_addr */
+ 0, 0, /* end of abbrev */
+ 0 /* no more abbrev */
+ },
+ .str = "\0" ".text\0" ".debug_info\0" ".debug_abbrev\0"
+ ".debug_frame\0" ".symtab\0" ".strtab\0" "code_gen_buffer",
+ };
+
+ /* We only need a single jit entry; statically allocate it. */
+ static struct jit_code_entry one_entry;
+
+ uintptr_t buf = (uintptr_t)buf_ptr;
+ size_t img_size = sizeof(struct ElfImage) + debug_frame_size;
+
+ img = g_malloc(img_size);
+ *img = img_template;
+ memcpy(img + 1, debug_frame, debug_frame_size);
+
+ img->phdr.p_vaddr = buf;
+ img->phdr.p_paddr = buf;
+ img->phdr.p_memsz = buf_size;
+
+ img->shdr[1].sh_name = find_string(img->str, ".text");
+ img->shdr[1].sh_addr = buf;
+ img->shdr[1].sh_size = buf_size;
+
+ img->shdr[2].sh_name = find_string(img->str, ".debug_info");
+ img->shdr[3].sh_name = find_string(img->str, ".debug_abbrev");
+
+ img->shdr[4].sh_name = find_string(img->str, ".debug_frame");
+ img->shdr[4].sh_size = debug_frame_size;
+
+ img->shdr[5].sh_name = find_string(img->str, ".symtab");
+ img->shdr[6].sh_name = find_string(img->str, ".strtab");
+
+ img->sym[1].st_name = find_string(img->str, "code_gen_buffer");
+ img->sym[1].st_value = buf;
+ img->sym[1].st_size = buf_size;
+
+ img->di.cu_low_pc = buf;
+ img->di.cu_high_pc = buf_size;
+ img->di.fn_low_pc = buf;
+ img->di.fn_high_pc = buf_size;
+
+#ifdef DEBUG_JIT
+ /* Enable this block to be able to debug the ELF image file creation.
+ One can use readelf, objdump, or other inspection utilities. */
+ {
+ FILE *f = fopen("/tmp/qemu.jit", "w+b");
+ if (f) {
+ if (fwrite(img, img_size, 1, f) != img_size) {
+ /* Avoid stupid unused return value warning for fwrite. */
+ }
+ fclose(f);
+ }
+ }
+#endif
+
+ one_entry.symfile_addr = img;
+ one_entry.symfile_size = img_size;
+
+ __jit_debug_descriptor.action_flag = JIT_REGISTER_FN;
+ __jit_debug_descriptor.relevant_entry = &one_entry;
+ __jit_debug_descriptor.first_entry = &one_entry;
+ __jit_debug_register_code();
+}
+#else
+/* No support for the feature. Provide the entry point expected by exec.c,
+ and implement the internal function we declared earlier. */
+
+static void tcg_register_jit_int(void *buf, size_t size,
+ void *debug_frame, size_t debug_frame_size)
+{
+}
+
+void tcg_register_jit(void *buf, size_t buf_size)
+{
+}
+#endif /* ELF_HOST_MACHINE */
diff --git a/tcg/tcg.h b/tcg/tcg.h
index 5f6c647..a83bddd 100644
--- a/tcg/tcg.h
+++ b/tcg/tcg.h
@@ -586,3 +586,5 @@ extern uint8_t code_gen_prologue[];
# define tcg_qemu_tb_exec(env, tb_ptr) \
((tcg_target_ulong (*)(void *, void *))code_gen_prologue)(env, tb_ptr)
#endif
+
+void tcg_register_jit(void *buf, size_t buf_size);
--
1.7.7.6