[RFA/sparc] Add handling of stack-check probes
Joel Brobecker
brobecker@adacore.com
Wed Mar 28 22:49:00 GMT 2007
Hello,
GDB is currently unable to unwind past stack-check probes that are
inserted by the compiler when compiling with -stack-check. The attached
patch adds handling for the sequences currently emitted by GCC. Eric
Botcazou told us that they can take 3 forms:
1. A single probe
sethi <some immediate>,%g1
sub %sp, %g1, %g1
clr [%g1 - some immediate]
2. A small number of probes (at most 5)
sethi <some immediate>,%g1
sub %sp, %g1, %g1
clr [%g1]
add %g1, -<some immediate>, %g1
clr [%g1]
[...]
add %g1, -<some immediate>, %g1
clr [%g1]
clr [%g1 - some immediate]
3. A probing loop
sethi <some immediate>,%g1
sub %sp, %g1, %g1
sethi <some immediate>, %g4
sub %g1, %g4, %g4
cmp %g1, %g4
be <disp>
add %g1, -<some immediate>, %g1
ba <disp>
clr [%g1]
clr [%g4 - some immediate]
2007-03-28 Joel Brobecker <brobecker@adacore.com>
* sparc-tdep.c (X_RS2): New macro.
(sparc_skip_stack_check): New function.
(sparc_analyze_prologue): Adjust PC past stack probing
sequence if necessary.
Tested on sparc-solaris, no regression.
OK to apply?
Thanks,
--
Joel
PS: Do other people think that it is simpler for the human brain to understand
if (pc >= current_pc)
than
if (current_pc <= pc)
In other words, the boundary value is put on the rhs of the condition,
and the variable value is put on the lhs... It's just an aesthetic
consideration, but I can change it if others agree.
-------------- next part --------------
Index: sparc-tdep.c
===================================================================
RCS file: /cvs/src/src/gdb/sparc-tdep.c,v
retrieving revision 1.178
diff -u -p -r1.178 sparc-tdep.c
--- sparc-tdep.c 27 Feb 2007 20:17:19 -0000 1.178
+++ sparc-tdep.c 28 Mar 2007 22:44:30 -0000
@@ -82,6 +82,7 @@ struct regset;
#define X_IMM22(i) ((i) & 0x3fffff)
#define X_OP3(i) (((i) >> 19) & 0x3f)
#define X_RS1(i) (((i) >> 14) & 0x1f)
+#define X_RS2(i) ((i) & 0x1f)
#define X_I(i) (((i) >> 13) & 1)
/* Sign extension macros. */
#define X_DISP22(i) ((X_IMM22 (i) ^ 0x200000) - 0x200000)
@@ -571,6 +572,156 @@ sparc_alloc_frame_cache (void)
return cache;
}
+/* GCC generates several well-known sequences of instructions at the begining
+ of each function prologue when compiling with -fstack-check. If one of
+ such sequences starts at START_PC, then return the address of the
+ instruction immediately past this sequence. Otherwise, return START_PC. */
+
+static CORE_ADDR
+sparc_skip_stack_check (const CORE_ADDR start_pc)
+{
+ CORE_ADDR pc = start_pc;
+ unsigned long insn;
+ int offset_stack_checking_sequence = 0;
+
+ /* With GCC, all stack checking sequences begin with the same two
+ instructions. */
+
+ /* sethi <some immediate>,%g1 */
+ insn = sparc_fetch_instruction (pc);
+ pc = pc + 4;
+ if (!(X_OP (insn) == 0 && X_OP2 (insn) == 0x4 && X_RD (insn) == 1))
+ return start_pc;
+
+ /* sub %sp, %g1, %g1 */
+ insn = sparc_fetch_instruction (pc);
+ pc = pc + 4;
+ if (!(X_OP (insn) == 2 && X_OP3 (insn) == 0x4 && !X_I(insn)
+ && X_RD (insn) == 1 && X_RS1 (insn) == 14 && X_RS2 (insn) == 1))
+ return start_pc;
+
+ insn = sparc_fetch_instruction (pc);
+ pc = pc + 4;
+
+ /* First possible sequence:
+ [first two instructions above]
+ clr [%g1 - some immediate] */
+
+ /* clr [%g1 - some immediate] */
+ if (X_OP (insn) == 3 && X_OP3(insn) == 0x4 && X_I(insn)
+ && X_RS1 (insn) == 1 && X_RD (insn) == 0)
+ {
+ /* Valid stack-check sequence, return the new PC. */
+ return pc;
+ }
+
+ /* Second possible sequence: A small number of probes.
+ [first two instructions above]
+ clr [%g1]
+ add %g1, -<some immediate>, %g1
+ clr [%g1]
+ [repeat the two instructions above any (small) number of times]
+ clr [%g1 - some immediate] */
+
+ /* clr [%g1] */
+ else if (X_OP (insn) == 3 && X_OP3(insn) == 0x4 && !X_I(insn)
+ && X_RS1 (insn) == 1 && X_RD (insn) == 0)
+ {
+ while (1)
+ {
+ /* add %g1, -<some immediate>, %g1 */
+ insn = sparc_fetch_instruction (pc);
+ pc = pc + 4;
+ if (!(X_OP (insn) == 2 && X_OP3(insn) == 0 && X_I(insn)
+ && X_RS1 (insn) == 1 && X_RD (insn) == 1))
+ break;
+
+ /* clr [%g1] */
+ insn = sparc_fetch_instruction (pc);
+ pc = pc + 4;
+ if (!(X_OP (insn) == 3 && X_OP3(insn) == 0x4 && !X_I(insn)
+ && X_RD (insn) == 0 && X_RS1 (insn) == 1))
+ return start_pc;
+ }
+
+ /* clr [%g1 - some immediate] */
+ if (!(X_OP (insn) == 3 && X_OP3(insn) == 0x4 && X_I(insn)
+ && X_RS1 (insn) == 1 && X_RD (insn) == 0))
+ return start_pc;
+
+ /* We found a valid stack-check sequence, return the new PC. */
+ return pc;
+ }
+
+ /* Third sequence: A probing loop.
+ [first two instructions above]
+ sethi <some immediate>, %g4
+ sub %g1, %g4, %g4
+ cmp %g1, %g4
+ be <disp>
+ add %g1, -<some immediate>, %g1
+ ba <disp>
+ clr [%g1]
+ clr [%g4 - some immediate] */
+
+ /* sethi <some immediate>, %g4 */
+ else if (X_OP (insn) == 0 && X_OP2 (insn) == 0x4 && X_RD (insn) == 4)
+ {
+ /* sub %g1, %g4, %g4 */
+ insn = sparc_fetch_instruction (pc);
+ pc = pc + 4;
+ if (!(X_OP (insn) == 2 && X_OP3 (insn) == 0x4 && !X_I(insn)
+ && X_RD (insn) == 4 && X_RS1 (insn) == 1 && X_RS2 (insn) == 4))
+ return start_pc;
+
+ /* cmp %g1, %g4 */
+ insn = sparc_fetch_instruction (pc);
+ pc = pc + 4;
+ if (!(X_OP (insn) == 2 && X_OP3 (insn) == 0x14 && !X_I(insn)
+ && X_RD (insn) == 0 && X_RS1 (insn) == 1 && X_RS2 (insn) == 4))
+ return start_pc;
+
+ /* be <disp> */
+ insn = sparc_fetch_instruction (pc);
+ pc = pc + 4;
+ if (!(X_OP (insn) == 0 && X_COND (insn) == 0x1))
+ return start_pc;
+
+ /* add %g1, -<some immediate>, %g1 */
+ insn = sparc_fetch_instruction (pc);
+ pc = pc + 4;
+ if (!(X_OP (insn) == 2 && X_OP3(insn) == 0 && X_I(insn)
+ && X_RS1 (insn) == 1 && X_RD (insn) == 1))
+ return start_pc;
+
+ /* ba <disp> */
+ insn = sparc_fetch_instruction (pc);
+ pc = pc + 4;
+ if (!(X_OP (insn) == 0 && X_COND (insn) == 0x8))
+ return start_pc;
+
+ /* clr [%g1] */
+ insn = sparc_fetch_instruction (pc);
+ pc = pc + 4;
+ if (!(X_OP (insn) == 3 && X_OP3(insn) == 0x4 && !X_I(insn)
+ && X_RD (insn) == 0 && X_RS1 (insn) == 1))
+ return start_pc;
+
+ /* clr [%g4 - some immediate] */
+ insn = sparc_fetch_instruction (pc);
+ pc = pc + 4;
+ if (!(X_OP (insn) == 3 && X_OP3(insn) == 0x4 && X_I(insn)
+ && X_RS1 (insn) == 4 && X_RD (insn) == 0))
+ return start_pc;
+
+ /* We found a valid stack-check sequence, return the new PC. */
+ return pc;
+ }
+
+ /* No stack check code in our prologue, return the start_pc. */
+ return start_pc;
+}
+
CORE_ADDR
sparc_analyze_prologue (CORE_ADDR pc, CORE_ADDR current_pc,
struct sparc_frame_cache *cache)
@@ -580,6 +731,8 @@ sparc_analyze_prologue (CORE_ADDR pc, CO
int offset = 0;
int dest = -1;
+ pc = sparc_skip_stack_check (pc);
+
if (current_pc <= pc)
return current_pc;
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