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Re: PATCH: Update x86 stack align analyzer
> Date: Wed, 6 Aug 2008 14:36:01 -0700
> From: "H.J. Lu" <hjl.tools@gmail.com>
>
> >> +/* GCC 4.4 and later, can put code in the prologue to realign the
> >> + stack pointer. Check whether PC points to such code, and update
> >> + CACHE accordingly. Return the first instruction after the code
> >> + sequence or CURRENT_PC, whichever is smaller. If we don't
> >> + recognize the code, return PC. */
> >
> > There are older versions of GCC that use at least method #2, so this
> > comment is a bit misleading.
>
> Gcc 4.1 can align stack to 16byte, but only for ia32, not for x86-64. We
> added this capability to gcc 4.4.
Ah ok, guess I confused amd64 with i386 there. Sorry 'bout that.
> >> +static CORE_ADDR
> >> +amd64_analyze_stack_align (CORE_ADDR pc, CORE_ADDR current_pc,
> >> + struct amd64_frame_cache *cache)
> >> +{
> >> + /* There are 3 code sequences to re-align stack:
> >> +
> >> + 1. Use %ebp:
> >> +
> >> + pushq %rbp
> >> + movq %rsp, %rbp
> >> + andq $-XXX, %rsp
> >
> > But this is basically the standard prologue sequence. I don't see why
> > you need to handle this sequence here, since it is already handled in
> > amd64_analyze_prologue().
>
> We need it to set saved_sp_reg.
I feel, rather strongly, that the stack align stuff stuff should only
deal with stack alignment done *before* a frame gets setup. I think
setting saved_sp_reg to -1, and proceeding as usual if it is still set
at that value after the stack alignment analysis, works just fine. I
also noticed a problem with your diff in that it doesn't use the
proper saved sp value if you do have a frame (not sure GCC actually
generates such code).
How about the attached diff? Does it work with GCC 4.4?
Index: amd64-tdep.c
===================================================================
RCS file: /cvs/src/src/gdb/amd64-tdep.c,v
retrieving revision 1.52
diff -u -p -r1.52 amd64-tdep.c
--- amd64-tdep.c 16 May 2008 00:27:22 -0000 1.52
+++ amd64-tdep.c 9 Aug 2008 11:56:43 -0000
@@ -680,6 +680,7 @@ struct amd64_frame_cache
/* Saved registers. */
CORE_ADDR saved_regs[AMD64_NUM_SAVED_REGS];
CORE_ADDR saved_sp;
+ int saved_sp_reg;
/* Do we have a frame? */
int frameless_p;
@@ -702,6 +703,7 @@ amd64_init_frame_cache (struct amd64_fra
for (i = 0; i < AMD64_NUM_SAVED_REGS; i++)
cache->saved_regs[i] = -1;
cache->saved_sp = 0;
+ cache->saved_sp_reg = -1;
/* Frameless until proven otherwise. */
cache->frameless_p = 1;
@@ -719,6 +721,179 @@ amd64_alloc_frame_cache (void)
return cache;
}
+/* GCC 4.4 and later, can put code in the prologue to realign the
+ stack pointer. Check whether PC points to such code, and update
+ CACHE accordingly. Return the first instruction after the code
+ sequence or CURRENT_PC, whichever is smaller. If we don't
+ recognize the code, return PC. */
+
+static CORE_ADDR
+amd64_analyze_stack_align (CORE_ADDR pc, CORE_ADDR current_pc,
+ struct amd64_frame_cache *cache)
+{
+ /* There are 2 code sequences to re-align stack before the frame
+ gets set up:
+
+ 1. Use a caller-saved saved register:
+
+ leaq 8(%rsp), %reg
+ andq $-XXX, %rsp
+ pushq -8(%reg)
+
+ 2. Use a callee-saved saved register:
+
+ pushq %reg
+ leaq 16(%rsp), %reg
+ andq $-XXX, %rsp
+ pushq -8(%reg)
+
+ "andq $-XXX, %rsp" can be either 4 bytes or 7 bytes:
+
+ 0x48 0x83 0xe4 0xf0 andq $-16, %rsp
+ 0x48 0x81 0xe4 0x00 0xff 0xff 0xff andq $-256, %rsp
+ */
+
+ gdb_byte buf[18];
+ int reg, r;
+ int offset, offset_and;
+ static int regnums[16] = {
+ AMD64_RAX_REGNUM, /* %rax */
+ AMD64_RCX_REGNUM, /* %rcx */
+ AMD64_RDX_REGNUM, /* %rdx */
+ AMD64_RBX_REGNUM, /* %rbx */
+ AMD64_RSP_REGNUM, /* %rsp */
+ AMD64_RBP_REGNUM, /* %rbp */
+ AMD64_RSI_REGNUM, /* %rsi */
+ AMD64_RDI_REGNUM, /* %rdi */
+ AMD64_R8_REGNUM, /* %r8 */
+ AMD64_R9_REGNUM, /* %r9 */
+ AMD64_R10_REGNUM, /* %r10 */
+ AMD64_R11_REGNUM, /* %r11 */
+ AMD64_R12_REGNUM, /* %r12 */
+ AMD64_R13_REGNUM, /* %r13 */
+ AMD64_R14_REGNUM, /* %r14 */
+ AMD64_R15_REGNUM, /* %r15 */
+ };
+
+ if (target_read_memory (pc, buf, sizeof buf))
+ return pc;
+
+ /* Check caller-saved saved register. The first instruction has
+ to be "leaq 8(%rsp), %reg". */
+ if ((buf[0] & 0xfb) == 0x48
+ && buf[1] == 0x8d
+ && buf[3] == 0x24
+ && buf[4] == 0x8)
+ {
+ /* MOD must be binary 10 and R/M must be binary 100. */
+ if ((buf[2] & 0xc7) != 0x44)
+ return pc;
+
+ /* REG has register number. */
+ reg = (buf[2] >> 3) & 7;
+
+ /* Check the REX.R bit. */
+ if (buf[0] == 0x4c)
+ reg += 8;
+
+ offset = 5;
+ }
+ else
+ {
+ /* Check callee-saved saved register. The first instruction
+ has to be "pushq %reg". */
+ reg = 0;
+ if ((buf[0] & 0xf8) == 0x50)
+ offset = 0;
+ else if ((buf[0] & 0xf6) == 0x40
+ && (buf[1] & 0xf8) == 0x50)
+ {
+ /* Check the REX.B bit. */
+ if ((buf[0] & 1) != 0)
+ reg = 8;
+
+ offset = 1;
+ }
+ else
+ return pc;
+
+ /* Get register. */
+ reg += buf[offset] & 0x7;
+
+ offset++;
+
+ /* The next instruction has to be "leaq 16(%rsp), %reg". */
+ if ((buf[offset] & 0xfb) != 0x48
+ || buf[offset + 1] != 0x8d
+ || buf[offset + 3] != 0x24
+ || buf[offset + 4] != 0x10)
+ return pc;
+
+ /* MOD must be binary 10 and R/M must be binary 100. */
+ if ((buf[offset + 2] & 0xc7) != 0x44)
+ return pc;
+
+ /* REG has register number. */
+ r = (buf[offset + 2] >> 3) & 7;
+
+ /* Check the REX.R bit. */
+ if (buf[offset] == 0x4c)
+ r += 8;
+
+ /* Registers in pushq and leaq have to be the same. */
+ if (reg != r)
+ return pc;
+
+ offset += 5;
+ }
+
+ /* Rigister can't be %rsp nor %rbp. */
+ if (reg == 4 || reg == 5)
+ return pc;
+
+ /* The next instruction has to be "andq $-XXX, %rsp". */
+ if (buf[offset] != 0x48
+ || buf[offset + 2] != 0xe4
+ || (buf[offset + 1] != 0x81 && buf[offset + 1] != 0x83))
+ return pc;
+
+ offset_and = offset;
+ offset += buf[offset + 1] == 0x81 ? 7 : 4;
+
+ /* The next instruction has to be "pushq -8(%reg)". */
+ r = 0;
+ if (buf[offset] == 0xff)
+ offset++;
+ else if ((buf[offset] & 0xf6) == 0x40
+ && buf[offset + 1] == 0xff)
+ {
+ /* Check the REX.B bit. */
+ if ((buf[offset] & 0x1) != 0)
+ r = 8;
+ offset += 2;
+ }
+ else
+ return pc;
+
+ /* 8bit -8 is 0xf8. REG must be binary 110 and MOD must be binary
+ 01. */
+ if (buf[offset + 1] != 0xf8
+ || (buf[offset] & 0xf8) != 0x70)
+ return pc;
+
+ /* R/M has register. */
+ r += buf[offset] & 7;
+
+ /* Registers in leaq and pushq have to be the same. */
+ if (reg != r)
+ return pc;
+
+ if (current_pc > pc + offset_and)
+ cache->saved_sp_reg = regnums[reg];
+
+ return min (pc + offset + 2, current_pc);
+}
+
/* Do a limited analysis of the prologue at PC and update CACHE
accordingly. Bail out early if CURRENT_PC is reached. Return the
address where the analysis stopped.
@@ -742,6 +917,8 @@ amd64_analyze_prologue (CORE_ADDR pc, CO
if (current_pc <= pc)
return current_pc;
+ pc = amd64_analyze_stack_align (pc, current_pc, cache);
+
op = read_memory_unsigned_integer (pc, 1);
if (op == 0x55) /* pushq %rbp */
@@ -804,6 +981,13 @@ amd64_frame_cache (struct frame_info *th
if (cache->pc != 0)
amd64_analyze_prologue (cache->pc, get_frame_pc (this_frame), cache);
+ if (cache->saved_sp_reg != -1)
+ {
+ /* Stack pointer has been saved. */
+ get_frame_register (this_frame, cache->saved_sp_reg, buf);
+ cache->saved_sp = extract_unsigned_integer(buf, 8);
+ }
+
if (cache->frameless_p)
{
/* We didn't find a valid frame. If we're at the start of a
@@ -813,8 +997,20 @@ amd64_frame_cache (struct frame_info *th
at the stack pointer. For truly "frameless" functions this
might work too. */
- get_frame_register (this_frame, AMD64_RSP_REGNUM, buf);
- cache->base = extract_unsigned_integer (buf, 8) + cache->sp_offset;
+ if (cache->saved_sp_reg != -1)
+ {
+ /* We're halfway aligning the stack. */
+ cache->base = ((cache->saved_sp - 8) & 0xfffffffffffffff0LL) - 8;
+ cache->saved_regs[AMD64_RIP_REGNUM] = cache->saved_sp - 8;
+
+ /* This will be added back below. */
+ cache->saved_regs[AMD64_RIP_REGNUM] -= cache->base;
+ }
+ else
+ {
+ get_frame_register (this_frame, AMD64_RSP_REGNUM, buf);
+ cache->base = extract_unsigned_integer (buf, 8) + cache->sp_offset;
+ }
}
else
{
@@ -828,8 +1024,10 @@ amd64_frame_cache (struct frame_info *th
/* For normal frames, %rip is stored at 8(%rbp). If we don't have a
frame we find it at the same offset from the reconstructed base
- address. */
- cache->saved_regs[AMD64_RIP_REGNUM] = 8;
+ address. If we're halfway aligning the stack, %rip is handled
+ differently (see above). */
+ if (!cache->frameless_p || cache->saved_sp_reg == -1)
+ cache->saved_regs[AMD64_RIP_REGNUM] = 8;
/* Adjust all the saved registers such that they contain addresses
instead of offsets. */
Index: amd64-tdep.h
===================================================================
RCS file: /cvs/src/src/gdb/amd64-tdep.h,v
retrieving revision 1.11
diff -u -p -r1.11 amd64-tdep.h
--- amd64-tdep.h 1 Jan 2008 22:53:09 -0000 1.11
+++ amd64-tdep.h 9 Aug 2008 11:56:43 -0000
@@ -39,8 +39,14 @@ enum amd64_regnum
AMD64_RDI_REGNUM, /* %rdi */
AMD64_RBP_REGNUM, /* %rbp */
AMD64_RSP_REGNUM, /* %rsp */
- AMD64_R8_REGNUM = 8, /* %r8 */
- AMD64_R15_REGNUM = 15, /* %r15 */
+ AMD64_R8_REGNUM, /* %r8 */
+ AMD64_R9_REGNUM, /* %r9 */
+ AMD64_R10_REGNUM, /* %r10 */
+ AMD64_R11_REGNUM, /* %r11 */
+ AMD64_R12_REGNUM, /* %r12 */
+ AMD64_R13_REGNUM, /* %r13 */
+ AMD64_R14_REGNUM, /* %r14 */
+ AMD64_R15_REGNUM, /* %r15 */
AMD64_RIP_REGNUM, /* %rip */
AMD64_EFLAGS_REGNUM, /* %eflags */
AMD64_CS_REGNUM, /* %cs */
Index: i386-tdep.c
===================================================================
RCS file: /cvs/src/src/gdb/i386-tdep.c,v
retrieving revision 1.261
diff -u -p -r1.261 i386-tdep.c
--- i386-tdep.c 3 Jul 2008 00:19:58 -0000 1.261
+++ i386-tdep.c 9 Aug 2008 11:56:44 -0000
@@ -518,7 +518,7 @@ struct i386_frame_cache
/* Saved registers. */
CORE_ADDR saved_regs[I386_NUM_SAVED_REGS];
CORE_ADDR saved_sp;
- int stack_align;
+ int saved_sp_reg;
int pc_in_eax;
/* Stack space reserved for local variables. */
@@ -545,7 +545,7 @@ i386_alloc_frame_cache (void)
for (i = 0; i < I386_NUM_SAVED_REGS; i++)
cache->saved_regs[i] = -1;
cache->saved_sp = 0;
- cache->stack_align = 0;
+ cache->saved_sp_reg = -1;
cache->pc_in_eax = 0;
/* Frameless until proven otherwise. */
@@ -707,37 +707,111 @@ static CORE_ADDR
i386_analyze_stack_align (CORE_ADDR pc, CORE_ADDR current_pc,
struct i386_frame_cache *cache)
{
- /* The register used by the compiler to perform the stack re-alignment
- is, in order of preference, either %ecx, %edx, or %eax. GCC should
- never use %ebx as it always treats it as callee-saved, whereas
- the compiler can only use caller-saved registers. */
- static const gdb_byte insns_ecx[10] = {
- 0x8d, 0x4c, 0x24, 0x04, /* leal 4(%esp), %ecx */
- 0x83, 0xe4, 0xf0, /* andl $-16, %esp */
- 0xff, 0x71, 0xfc /* pushl -4(%ecx) */
- };
- static const gdb_byte insns_edx[10] = {
- 0x8d, 0x54, 0x24, 0x04, /* leal 4(%esp), %edx */
- 0x83, 0xe4, 0xf0, /* andl $-16, %esp */
- 0xff, 0x72, 0xfc /* pushl -4(%edx) */
- };
- static const gdb_byte insns_eax[10] = {
- 0x8d, 0x44, 0x24, 0x04, /* leal 4(%esp), %eax */
- 0x83, 0xe4, 0xf0, /* andl $-16, %esp */
- 0xff, 0x70, 0xfc /* pushl -4(%eax) */
+ /* There are 2 code sequences to re-align stack before the frame
+ gets set up:
+
+ 1. Use a caller-saved saved register:
+
+ leal 4(%esp), %reg
+ andl $-XXX, %esp
+ pushl -4(%reg)
+
+ 2. Use a callee-saved saved register:
+
+ pushl %reg
+ leal 8(%esp), %reg
+ andl $-XXX, %esp
+ pushl -4(%reg)
+
+ "andl $-XXX, %esp" can be either 3 bytes or 6 bytes:
+
+ 0x83 0xe4 0xf0 andl $-16, %esp
+ 0x81 0xe4 0x00 0xff 0xff 0xff andl $-256, %esp
+ */
+
+ gdb_byte buf[14];
+ int reg;
+ int offset, offset_and;
+ static int regnums[8] = {
+ I386_EAX_REGNUM, /* %eax */
+ I386_ECX_REGNUM, /* %ecx */
+ I386_EDX_REGNUM, /* %edx */
+ I386_EBX_REGNUM, /* %ebx */
+ I386_ESP_REGNUM, /* %esp */
+ I386_EBP_REGNUM, /* %ebp */
+ I386_ESI_REGNUM, /* %esi */
+ I386_EDI_REGNUM /* %edi */
};
- gdb_byte buf[10];
- if (target_read_memory (pc, buf, sizeof buf)
- || (memcmp (buf, insns_ecx, sizeof buf) != 0
- && memcmp (buf, insns_edx, sizeof buf) != 0
- && memcmp (buf, insns_eax, sizeof buf) != 0))
+ if (target_read_memory (pc, buf, sizeof buf))
+ return pc;
+
+ /* Check caller-saved saved register. The first instruction has
+ to be "leal 4(%esp), %reg". */
+ if (buf[0] == 0x8d && buf[2] == 0x24 && buf[3] == 0x4)
+ {
+ /* MOD must be binary 10 and R/M must be binary 100. */
+ if ((buf[1] & 0xc7) != 0x44)
+ return pc;
+
+ /* REG has register number. */
+ reg = (buf[1] >> 3) & 7;
+ offset = 4;
+ }
+ else
+ {
+ /* Check callee-saved saved register. The first instruction
+ has to be "pushl %reg". */
+ if ((buf[0] & 0xf8) != 0x50)
+ return pc;
+
+ /* Get register. */
+ reg = buf[0] & 0x7;
+
+ /* The next instruction has to be "leal 8(%esp), %reg". */
+ if (buf[1] != 0x8d || buf[3] != 0x24 || buf[4] != 0x8)
+ return pc;
+
+ /* MOD must be binary 10 and R/M must be binary 100. */
+ if ((buf[2] & 0xc7) != 0x44)
+ return pc;
+
+ /* REG has register number. Registers in pushl and leal have to
+ be the same. */
+ if (reg != ((buf[2] >> 3) & 7))
+ return pc;
+
+ offset = 5;
+ }
+
+ /* Rigister can't be %esp nor %ebp. */
+ if (reg == 4 || reg == 5)
+ return pc;
+
+ /* The next instruction has to be "andl $-XXX, %esp". */
+ if (buf[offset + 1] != 0xe4
+ || (buf[offset] != 0x81 && buf[offset] != 0x83))
+ return pc;
+
+ offset_and = offset;
+ offset += buf[offset] == 0x81 ? 6 : 3;
+
+ /* The next instruction has to be "pushl -4(%reg)". 8bit -4 is
+ 0xfc. REG must be binary 110 and MOD must be binary 01. */
+ if (buf[offset] != 0xff
+ || buf[offset + 2] != 0xfc
+ || (buf[offset + 1] & 0xf8) != 0x70)
+ return pc;
+
+ /* R/M has register. Registers in leal and pushl have to be the
+ same. */
+ if (reg != (buf[offset + 1] & 7))
return pc;
- if (current_pc > pc + 4)
- cache->stack_align = 1;
+ if (current_pc > pc + offset_and)
+ cache->saved_sp_reg = regnums[reg];
- return min (pc + 10, current_pc);
+ return min (pc + offset + 3, current_pc);
}
/* Maximum instruction length we need to handle. */
@@ -1241,10 +1315,10 @@ i386_frame_cache (struct frame_info *thi
if (cache->pc != 0)
i386_analyze_prologue (cache->pc, get_frame_pc (this_frame), cache);
- if (cache->stack_align)
+ if (cache->saved_sp_reg != -1)
{
- /* Saved stack pointer has been saved in %ecx. */
- get_frame_register (this_frame, I386_ECX_REGNUM, buf);
+ /* Saved stack pointer has been saved. */
+ get_frame_register (this_frame, cache->saved_sp_reg, buf);
cache->saved_sp = extract_unsigned_integer(buf, 4);
}
@@ -1258,7 +1332,7 @@ i386_frame_cache (struct frame_info *thi
frame by looking at the stack pointer. For truly "frameless"
functions this might work too. */
- if (cache->stack_align)
+ if (cache->saved_sp_reg != -1)
{
/* We're halfway aligning the stack. */
cache->base = ((cache->saved_sp - 4) & 0xfffffff0) - 4;