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Re: [RFA] i386/amd64 displaced stepping fixes
- From: Doug Evans <dje at google dot com>
- To: gdb-patches at sourceware dot org
- Date: Fri, 6 Feb 2009 16:12:41 -0800
- Subject: Re: [RFA] i386/amd64 displaced stepping fixes
- References: <20090202024654.8BD461C7A19@localhost>
Ping.
On Sun, Feb 1, 2009 at 6:46 PM, Doug Evans <dje@google.com> wrote:
> Hi. This patch fixes a few things in i386/amd64 displaced stepping.
>
> 1) Assuming(!) it is correct to not back up the pc when stepping over an int3,
> this updates both arches' fixup routines to not do this.
> 2) Adds prefix scanning to the i386 support.
> These prefixes are normally not present, but I think gdb shouldn't
> ignore them.
> 3) Adds handling for more 3-byte opcodes in the amd64 port.
> 4) Adds new tests to the i386 and amd64 displaced stepping tests.
> 5) minor cleanups like constifying the `insn' parameter to the i386
> instruction predicates
>
> Question: There's both i386_skip_prefixes and amd64_skip_prefixes
> functions. Arguably there should be only one, though they currently
> have different signatures. If there's a strong feeling that
> there should be only one, I can rewrite the patch to use only one function,
> but I'm not sure where to put it. Suggestions?
>
> Ok to check in?
>
> 2009-02-01 Doug Evans <dje@google.com>
>
> * amd64-tdep.c (amd64_skip_prefixes): Renamed from skip_prefixes.
> All callers updated.
> (amd64_get_insn_details): Handle more 3-byte opcode insns.
> (amd64_breakpoint_p): Delete.
> (amd64_displaced_step_fixup): When fixing up after stepping an int3,
> don't back up pc to the start of the int3.
> * i386-tdep.c: #include opcode/i386.h.
> (i386_skip_prefixes): New function.
> (i386_absolute_jmp_p): Constify argument.
> (i386_absolute_call_p,i386_ret_p,i386_call_p,i386_syscall_p): Ditto.
> (i386_breakpoint_p): Delete.
> (i386_displaced_step_fixup): Handle unnecessary or redundant prefixes.
> When fixing up after stepping an int3, don't back up pc to the start
> of the int3.
>
> * gdb.arch/amd64-disp-step.S (test_int3): New test.
> * gdb.arch/amd64-disp-step.exp (test_int3): New test.
> * gdb.arch/i386-disp-step.S (test_prefixed_abs_jump): New test.
> (test_prefixed_syscall,test_int3): New tests.
> * gdb.arch/i386-disp-step.exp (test_prefixed_abs_jump): New test.
> (test_prefixed_syscall,test_int3): New tests.
>
> Index: amd64-tdep.c
> ===================================================================
> RCS file: /cvs/src/src/gdb/amd64-tdep.c,v
> retrieving revision 1.57
> diff -u -p -u -p -r1.57 amd64-tdep.c
> --- amd64-tdep.c 29 Jan 2009 00:29:56 -0000 1.57
> +++ amd64-tdep.c 2 Feb 2009 02:33:36 -0000
> @@ -805,7 +805,7 @@ rex_prefix_p (gdb_byte pfx)
> about falling off the end of the buffer. */
>
> static gdb_byte *
> -skip_prefixes (gdb_byte *insn)
> +amd64_skip_prefixes (gdb_byte *insn)
> {
> while (1)
> {
> @@ -974,7 +974,7 @@ amd64_get_insn_details (gdb_byte *insn,
> details->modrm_offset = -1;
>
> /* Skip legacy instruction prefixes. */
> - insn = skip_prefixes (insn);
> + insn = amd64_skip_prefixes (insn);
>
> /* Skip REX instruction prefix. */
> if (rex_prefix_p (*insn))
> @@ -992,13 +992,21 @@ amd64_get_insn_details (gdb_byte *insn,
> need_modrm = twobyte_has_modrm[*insn];
>
> /* Check for three-byte opcode. */
> - if (*insn == 0x38 || *insn == 0x3a)
> + switch (*insn)
> {
> + case 0x24:
> + case 0x25:
> + case 0x38:
> + case 0x3a:
> + case 0x7a:
> + case 0x7b:
> ++insn;
> details->opcode_len = 3;
> + break;
> + default:
> + details->opcode_len = 2;
> + break;
> }
> - else
> - details->opcode_len = 2;
> }
> else
> {
> @@ -1217,14 +1225,6 @@ amd64_call_p (const struct amd64_insn *d
> return 0;
> }
>
> -static int
> -amd64_breakpoint_p (const struct amd64_insn *details)
> -{
> - const gdb_byte *insn = &details->raw_insn[details->opcode_offset];
> -
> - return insn[0] == 0xcc; /* int 3 */
> -}
> -
> /* Return non-zero if INSN is a system call, and set *LENGTHP to its
> length in bytes. Otherwise, return zero. */
>
> @@ -1323,21 +1323,6 @@ amd64_displaced_step_fixup (struct gdbar
> {
> ULONGEST rip = orig_rip - insn_offset;
>
> - /* If we have stepped over a breakpoint, set %rip to
> - point at the breakpoint instruction itself.
> -
> - (gdbarch_decr_pc_after_break was never something the core
> - of GDB should have been concerned with; arch-specific
> - code should be making PC values consistent before
> - presenting them to GDB.) */
> - if (amd64_breakpoint_p (insn_details))
> - {
> - if (debug_displaced)
> - fprintf_unfiltered (gdb_stdlog,
> - "displaced: stepped breakpoint\n");
> - rip--;
> - }
> -
> regcache_cooked_write_unsigned (regs, AMD64_RIP_REGNUM, rip);
>
> if (debug_displaced)
> Index: i386-tdep.c
> ===================================================================
> RCS file: /cvs/src/src/gdb/i386-tdep.c,v
> retrieving revision 1.267
> diff -u -p -u -p -r1.267 i386-tdep.c
> --- i386-tdep.c 3 Jan 2009 05:57:51 -0000 1.267
> +++ i386-tdep.c 2 Feb 2009 02:33:37 -0000
> @@ -20,6 +20,7 @@
> along with this program. If not, see <http://www.gnu.org/licenses/>. */
>
> #include "defs.h"
> +#include "opcode/i386.h"
> #include "arch-utils.h"
> #include "command.h"
> #include "dummy-frame.h"
> @@ -278,9 +279,44 @@ i386_breakpoint_from_pc (struct gdbarch
>
> /* Displaced instruction handling. */
>
> +/* Skip the legacy instruction prefixes in INSN.
> + Not all prefixes are valid for any particular insn
> + but we needn't care, the insn will fault if it's invalid.
> + The result is a pointer to the first opcode byte,
> + or NULL if we run off the end of the buffer. */
> +
> +static gdb_byte *
> +i386_skip_prefixes (gdb_byte *insn, size_t max_len)
> +{
> + gdb_byte *end = insn + max_len;
> +
> + while (insn < end)
> + {
> + switch (*insn)
> + {
> + case DATA_PREFIX_OPCODE:
> + case ADDR_PREFIX_OPCODE:
> + case CS_PREFIX_OPCODE:
> + case DS_PREFIX_OPCODE:
> + case ES_PREFIX_OPCODE:
> + case FS_PREFIX_OPCODE:
> + case GS_PREFIX_OPCODE:
> + case SS_PREFIX_OPCODE:
> + case LOCK_PREFIX_OPCODE:
> + case REPE_PREFIX_OPCODE:
> + case REPNE_PREFIX_OPCODE:
> + ++insn;
> + continue;
> + default:
> + return insn;
> + }
> + }
> +
> + return NULL;
> +}
>
> static int
> -i386_absolute_jmp_p (gdb_byte *insn)
> +i386_absolute_jmp_p (const gdb_byte *insn)
> {
> /* jmp far (absolute address in operand) */
> if (insn[0] == 0xea)
> @@ -301,7 +337,7 @@ i386_absolute_jmp_p (gdb_byte *insn)
> }
>
> static int
> -i386_absolute_call_p (gdb_byte *insn)
> +i386_absolute_call_p (const gdb_byte *insn)
> {
> /* call far, absolute */
> if (insn[0] == 0x9a)
> @@ -322,7 +358,7 @@ i386_absolute_call_p (gdb_byte *insn)
> }
>
> static int
> -i386_ret_p (gdb_byte *insn)
> +i386_ret_p (const gdb_byte *insn)
> {
> switch (insn[0])
> {
> @@ -339,7 +375,7 @@ i386_ret_p (gdb_byte *insn)
> }
>
> static int
> -i386_call_p (gdb_byte *insn)
> +i386_call_p (const gdb_byte *insn)
> {
> if (i386_absolute_call_p (insn))
> return 1;
> @@ -351,16 +387,11 @@ i386_call_p (gdb_byte *insn)
> return 0;
> }
>
> -static int
> -i386_breakpoint_p (gdb_byte *insn)
> -{
> - return insn[0] == 0xcc; /* int 3 */
> -}
> -
> /* Return non-zero if INSN is a system call, and set *LENGTHP to its
> length in bytes. Otherwise, return zero. */
> +
> static int
> -i386_syscall_p (gdb_byte *insn, ULONGEST *lengthp)
> +i386_syscall_p (const gdb_byte *insn, ULONGEST *lengthp)
> {
> if (insn[0] == 0xcd)
> {
> @@ -373,6 +404,7 @@ i386_syscall_p (gdb_byte *insn, ULONGEST
>
> /* Fix up the state of registers and memory after having single-stepped
> a displaced instruction. */
> +
> void
> i386_displaced_step_fixup (struct gdbarch *gdbarch,
> struct displaced_step_closure *closure,
> @@ -388,6 +420,8 @@ i386_displaced_step_fixup (struct gdbarc
> /* Since we use simple_displaced_step_copy_insn, our closure is a
> copy of the instruction. */
> gdb_byte *insn = (gdb_byte *) closure;
> + /* The start of the insn, needed in case we see some prefixes. */
> + gdb_byte *insn_start = insn;
>
> if (debug_displaced)
> fprintf_unfiltered (gdb_stdlog,
> @@ -401,6 +435,18 @@ i386_displaced_step_fixup (struct gdbarc
>
> /* Relocate the %eip, if necessary. */
>
> + /* The instruction recognizers we use assume any leading prefixes
> + have been skipped. */
> + {
> + /* This is the size of the buffer in closure. */
> + size_t max_insn_len = gdbarch_max_insn_length (gdbarch);
> + gdb_byte *opcode = i386_skip_prefixes (insn, max_insn_len);
> + /* If there are too many prefixes, just ignore the insn.
> + It will fault when run. */
> + if (opcode != NULL)
> + insn = opcode;
> + }
> +
> /* Except in the case of absolute or indirect jump or call
> instructions, or a return instruction, the new eip is relative to
> the displaced instruction; make it relative. Well, signal
> @@ -430,7 +476,7 @@ i386_displaced_step_fixup (struct gdbarc
> it unrelocated. Goodness help us if there are PC-relative
> system calls. */
> if (i386_syscall_p (insn, &insn_len)
> - && orig_eip != to + insn_len)
> + && orig_eip != to + (insn - insn_start) + insn_len)
> {
> if (debug_displaced)
> fprintf_unfiltered (gdb_stdlog,
> @@ -441,21 +487,6 @@ i386_displaced_step_fixup (struct gdbarc
> {
> ULONGEST eip = (orig_eip - insn_offset) & 0xffffffffUL;
>
> - /* If we have stepped over a breakpoint, set the %eip to
> - point at the breakpoint instruction itself.
> -
> - (gdbarch_decr_pc_after_break was never something the core
> - of GDB should have been concerned with; arch-specific
> - code should be making PC values consistent before
> - presenting them to GDB.) */
> - if (i386_breakpoint_p (insn))
> - {
> - if (debug_displaced)
> - fprintf_unfiltered (gdb_stdlog,
> - "displaced: stepped breakpoint\n");
> - eip--;
> - }
> -
> regcache_cooked_write_unsigned (regs, I386_EIP_REGNUM, eip);
>
> if (debug_displaced)
> @@ -493,8 +524,6 @@ i386_displaced_step_fixup (struct gdbarc
> paddr_nz (retaddr));
> }
> }
> -
> -
>
> #ifdef I386_REGNO_TO_SYMMETRY
> #error "The Sequent Symmetry is no longer supported."
> Index: testsuite/gdb.arch/amd64-disp-step.S
> ===================================================================
> RCS file: /cvs/src/src/gdb/testsuite/gdb.arch/amd64-disp-step.S,v
> retrieving revision 1.1
> diff -u -p -u -p -r1.1 amd64-disp-step.S
> --- testsuite/gdb.arch/amd64-disp-step.S 29 Jan 2009 00:29:57 -0000 1.1
> +++ testsuite/gdb.arch/amd64-disp-step.S 2 Feb 2009 02:33:37 -0000
> @@ -23,6 +23,8 @@
> main:
> nop
>
> +/***********************************************/
> +
> /* test call/ret */
>
> .global test_call
> @@ -33,6 +35,8 @@ test_call:
> test_ret_end:
> nop
>
> +/***********************************************/
> +
> /* test abs-jmp/rep-ret */
>
> test_abs_jmp_setup:
> @@ -48,6 +52,8 @@ test_abs_jmp_return:
> test_rep_ret_end:
> nop
>
> +/***********************************************/
> +
> /* test syscall */
>
> .global test_syscall
> @@ -58,6 +64,24 @@ test_syscall:
> test_syscall_end:
> nop
>
> +/***********************************************/
> +
> +/* Test stepping over int3.
> + The prefixes are pointless, but it's possible, so we exercise it. */
> +
> + nop
> + .global test_int3
> +test_int3:
> + repz
> + repz
> + int3
> + nop
> + .global test_int3_end
> +test_int3_end:
> + nop
> +
> +/***********************************************/
> +
> /* test rip-relative
> GDB picks a spare register to hold the rip-relative address.
> Exercise all the possibilities (rax-rdi, sans rsp). */
> @@ -118,6 +142,8 @@ test_rip_rdi_end:
>
> answer: .8byte 42
>
> +/***********************************************/
> +
> /* all done */
>
> done:
> @@ -139,6 +165,8 @@ test_call_end:
> test_ret:
> ret
>
> +/***********************************************/
> +
> /* subroutine to help test abs-jmp/rep-ret */
>
> test_abs_jmp_subr:
> Index: testsuite/gdb.arch/amd64-disp-step.exp
> ===================================================================
> RCS file: /cvs/src/src/gdb/testsuite/gdb.arch/amd64-disp-step.exp,v
> retrieving revision 1.1
> diff -u -p -u -p -r1.1 amd64-disp-step.exp
> --- testsuite/gdb.arch/amd64-disp-step.exp 29 Jan 2009 00:29:57 -0000 1.1
> +++ testsuite/gdb.arch/amd64-disp-step.exp 2 Feb 2009 02:33:37 -0000
> @@ -141,6 +141,29 @@ gdb_test "continue" \
>
> ##########################################
>
> +# int3 (with prefixes)
> +# These don't occur in normal code, but gdb should still DTRT.
> +
> +gdb_test "break test_int3" \
> + "Breakpoint.*at.* file .*$srcfile, line.*" \
> + "break test_int3"
> +gdb_test "break test_int3_end" \
> + "Breakpoint.*at.* file .*$srcfile, line.*" \
> + "break test_int3_end"
> +
> +gdb_test "continue" \
> + "Continuing.*Breakpoint.*, test_int3 ().*" \
> + "continue to test_int3"
> +# FIXME: Single stepping over an int3 currently doesn't generate a SIGTRAP.
> +#gdb_test "continue" \
> +# "Continuing.*SIGTRAP.*" \
> +# "continue to test_int3_SIGTRAP"
> +gdb_test "continue" \
> + "Continuing.*Breakpoint.*, test_int3_end ().*" \
> + "continue to test_int3_end"
> +
> +##########################################
> +
> # Test rip-relative.
> # GDB picks a spare register to hold the rip-relative address.
> # Exercise all the possibilities (rax-rdi, sans rsp).
> Index: testsuite/gdb.arch/i386-disp-step.S
> ===================================================================
> RCS file: /cvs/src/src/gdb/testsuite/gdb.arch/i386-disp-step.S,v
> retrieving revision 1.1
> diff -u -p -u -p -r1.1 i386-disp-step.S
> --- testsuite/gdb.arch/i386-disp-step.S 29 Jan 2009 00:29:57 -0000 1.1
> +++ testsuite/gdb.arch/i386-disp-step.S 2 Feb 2009 02:33:37 -0000
> @@ -23,8 +23,11 @@
> main:
> nop
>
> -/* test call/ret */
> +/***********************************************/
> +
> +/* Test call/ret. */
>
> + nop
> .global test_call
> test_call:
> call test_call_subr
> @@ -33,16 +36,72 @@ test_call:
> test_ret_end:
> nop
>
> -/* test syscall */
> +/***********************************************/
> +
> +/* Absolute jump with leading prefixes.
> + These don't occur in normal code, but gdb should still DTRT. */
> +
> + nop
> + .global test_prefixed_abs_jump
> +test_prefixed_abs_jump:
> + ds
> + jmp *test_prefixed_abs_jump_addr
> + .data
> +test_prefixed_abs_jump_addr:
> + .4byte test_prefixed_abs_jump_target
> + .text
> +test_prefixed_abs_jump_target:
> + nop
> + .global test_prefixed_abs_jump_end
> +test_prefixed_abs_jump_end:
> + nop
> +
> +/***********************************************/
> +
> +/* Test syscall. */
>
> - .global test_syscall
> mov $0x14,%eax /* getpid */
> + .global test_syscall
> test_syscall:
> int $0x80
> nop
> + .global test_syscall_end
> test_syscall_end:
> nop
>
> +/***********************************************/
> +
> +/* Test syscall again, this time with a prefix.
> + These don't occur in normal code, but gdb should still DTRT. */
> +
> + mov $0x14,%eax /* getpid */
> + .global test_prefixed_syscall
> +test_prefixed_syscall:
> + repnz
> + int $0x80
> + nop
> + .global test_prefixed_syscall_end
> +test_prefixed_syscall_end:
> + nop
> +
> +/***********************************************/
> +
> +/* Test stepping over int3.
> + The prefixes are pointless, but it's possible, so we exercise it. */
> +
> + nop
> + .global test_int3
> +test_int3:
> + repz
> + repz
> + int3
> + nop
> + .global test_int3_end
> +test_int3_end:
> + nop
> +
> +/***********************************************/
> +
> /* all done */
>
> pushl $0
> Index: testsuite/gdb.arch/i386-disp-step.exp
> ===================================================================
> RCS file: /cvs/src/src/gdb/testsuite/gdb.arch/i386-disp-step.exp,v
> retrieving revision 1.1
> diff -u -p -u -p -r1.1 i386-disp-step.exp
> --- testsuite/gdb.arch/i386-disp-step.exp 29 Jan 2009 00:29:57 -0000 1.1
> +++ testsuite/gdb.arch/i386-disp-step.exp 2 Feb 2009 02:33:37 -0000
> @@ -89,6 +89,25 @@ gdb_test "continue" \
>
> ##########################################
>
> +# Absolute jump with leading prefixes.
> +# These don't occur in normal code, but gdb should still DTRT.
> +
> +gdb_test "break test_prefixed_abs_jump" \
> + "Breakpoint.*at.* file .*$srcfile, line.*" \
> + "break test_prefixed_abs_jump"
> +gdb_test "break test_prefixed_abs_jump_end" \
> + "Breakpoint.*at.* file .*$srcfile, line.*" \
> + "break test_prefixed_abs_jump_end"
> +
> +gdb_test "continue" \
> + "Continuing.*Breakpoint.*, test_prefixed_abs_jump ().*" \
> + "continue to test_prefixed_abs_jump"
> +gdb_test "continue" \
> + "Continuing.*Breakpoint.*, test_prefixed_abs_jump_end ().*" \
> + "continue to test_prefixed_abs_jump_end"
> +
> +##########################################
> +
> # Test syscall.
>
> gdb_test "break test_syscall" \
> @@ -107,6 +126,48 @@ gdb_test "continue" \
>
> ##########################################
>
> +# Test prefixed syscall.
> +# These don't occur in normal code, but gdb should still DTRT.
> +
> +gdb_test "break test_prefixed_syscall" \
> + "Breakpoint.*at.* file .*$srcfile, line.*" \
> + "break test_prefixed_syscall"
> +gdb_test "break test_prefixed_syscall_end" \
> + "Breakpoint.*at.* file .*$srcfile, line.*" \
> + "break test_prefixed_syscall_end"
> +
> +gdb_test "continue" \
> + "Continuing.*Breakpoint.*, test_prefixed_syscall ().*" \
> + "continue to test_prefixed_syscall"
> +gdb_test "continue" \
> + "Continuing.*Breakpoint.*, test_prefixed_syscall_end ().*" \
> + "continue to test_prefixed_syscall_end"
> +
> +##########################################
> +
> +# int3 (with prefixes)
> +# These don't occur in normal code, but gdb should still DTRT.
> +
> +gdb_test "break test_int3" \
> + "Breakpoint.*at.* file .*$srcfile, line.*" \
> + "break test_int3"
> +gdb_test "break test_int3_end" \
> + "Breakpoint.*at.* file .*$srcfile, line.*" \
> + "break test_int3_end"
> +
> +gdb_test "continue" \
> + "Continuing.*Breakpoint.*, test_int3 ().*" \
> + "continue to test_int3"
> +# FIXME: Single stepping over an int3 currently doesn't generate a SIGTRAP.
> +#gdb_test "continue" \
> +# "Continuing.*SIGTRAP.*" \
> +# "continue to test_int3_SIGTRAP"
> +gdb_test "continue" \
> + "Continuing.*Breakpoint.*, test_int3_end ().*" \
> + "continue to test_int3_end"
> +
> +##########################################
> +
> # Done, run program to exit.
>
> gdb_continue_to_end "i386-disp-step"
>