| Message ID | CADnVucCiDSYkMaSLht06fPVW8LZHpX513PQoKO-oOPAie-N8mQ@mail.gmail.com |
|---|---|
| State | New |
| Headers | show |
On 12/02/16 14:56, Charles Baylis wrote: > When compiling with -mlong-calls and -pg, calls to the __gnu_mcount_nc > function are not generated as long calls. > > This is encountered when building an allyesconfig Linux kernel because > the Linux build system generates very large sections by partial > linking a large number of object files. This causes link failures, > which don't go away with -mlong-calls due to this bug. (However, with > this patch linking still fails due to calls in inline asm) > > For example: > > extern void g(void); > int f() { g(); return 0; } > > compiles to: > > push {r4, lr} > push {lr} > bl __gnu_mcount_nc ;// not a long call Ouch! That's left the stack misaligned. That might be OK iff we can assume __gnu_mcount_nc is not required to be an ABI-conforming call. > ldr r3, .L2 > blx r3 ;// a long call to g() > mov r0, #0 > pop {r4, pc} > > The call to __gnu_mcount_nc is generated from ARM_FUNCTION_PROFILER in > config/arm/bpabi.h. > > For targets without MOVW/MOVT, the long call sequence requires a load > from the literal pool, and it is too late to set up a literal pool > entry from within ARM_FUNCTION_PROFILER. My approach to fix this is to > modify the prologue generation to load the address of __gnu_mcount_nc > into ip, so that it is ready when the call is generated. > > This patch only implements the fix for ARM and Thumb-2. A similar fix > is possible for Thumb-1, but requires more slightly complex changes to > the prologue generation to make sure there is a low register > available. Can you check this with a nested function? Eg. int f() { int a; int b () { return a+1; } a = 1; a += b(); assert (a == 3); return a; } I think this will break with your patch since the closure will be passed in IP. R. > > This feels like a bit of a hack to me, so ideas for a cleaner solution > are welcome, if none, is this acceptable for trunk now, or should it > wait until GCC 7? > > > 0001-ARM-PR69770-fix-mlong-calls-with-pg.patch > > > From 34993396a43fcfc263db5b02b2d1837c490f52ad Mon Sep 17 00:00:00 2001 > From: Charles Baylis <charles.baylis@linaro.org> > Date: Thu, 11 Feb 2016 18:07:00 +0000 > Subject: [PATCH] [ARM] PR69770 fix -mlong-calls with -pg > > gcc/ChangeLog: > > 2016-02-12 Charles Baylis <charles.baylis@linaro.org> > > * config/arm/arm.c (arm_expand_prologue): Load address of > __gnu_mcount_nc in r12 if profiling and long calls are enabled. > * config/arm/bpabi.h (ARM_FUNCTION_PROFILER): Emit long call to > __gnu_mcount_nc long calls are enabled. > (ARM_FUNCTION_PROFILER_SUPPORTS_LONG_CALLS): New define. > > gcc/testsuite/ChangeLog: > > 2016-02-12 Charles Baylis <charles.baylis@linaro.org> > > * gcc.target/arm/pr69770.c: New test. > > Change-Id: I4c639a5edf32fa8c67324d37faee1cb4ddd57a5c > > diff --git a/gcc/config/arm/arm.c b/gcc/config/arm/arm.c > index 27aecf7..9ce9a58 100644 > --- a/gcc/config/arm/arm.c > +++ b/gcc/config/arm/arm.c > @@ -21739,6 +21739,15 @@ arm_expand_prologue (void) > arm_load_pic_register (mask); > } > > + if (crtl->profile && TARGET_LONG_CALLS > + && ARM_FUNCTION_PROFILER_SUPPORTS_LONG_CALLS) > + { > + rtx tmp = gen_rtx_SET (gen_rtx_REG (SImode, IP_REGNUM), > + gen_rtx_SYMBOL_REF (Pmode, "__gnu_mcount_nc")); > + emit_insn (tmp); > + emit_insn (gen_rtx_USE (VOIDmode, gen_rtx_REG (SImode, IP_REGNUM))); > + } > + > /* If we are profiling, make sure no instructions are scheduled before > the call to mcount. Similarly if the user has requested no > scheduling in the prolog. Similarly if we want non-call exceptions > diff --git a/gcc/config/arm/bpabi.h b/gcc/config/arm/bpabi.h > index 82128ef..b734a24 100644 > --- a/gcc/config/arm/bpabi.h > +++ b/gcc/config/arm/bpabi.h > @@ -173,11 +173,21 @@ > > #undef NO_PROFILE_COUNTERS > #define NO_PROFILE_COUNTERS 1 > +#undef ARM_FUNCTION_PROFILER_SUPPORTS_LONG_CALLS > +#define ARM_FUNCTION_PROFILER_SUPPORTS_LONG_CALLS 1 > #undef ARM_FUNCTION_PROFILER > #define ARM_FUNCTION_PROFILER(STREAM, LABELNO) \ > { \ > - fprintf (STREAM, "\tpush\t{lr}\n"); \ > - fprintf (STREAM, "\tbl\t__gnu_mcount_nc\n"); \ > + if (TARGET_LONG_CALLS && TARGET_32BIT) \ > + { \ > + fprintf (STREAM, "\tpush\t{lr}\n"); \ > + /* arm_expand_prolog() has already set up ip to contain the */ \ > + /* address of __gnu_mcount_nc. */ \ > + fprintf (STREAM, "\tblx\tip\n"); \ > + } else { \ > + fprintf (STREAM, "\tpush\t{lr}\n"); \ > + fprintf (STREAM, "\tbl\t__gnu_mcount_nc\n"); \ > + } \ > } > > #undef SUBTARGET_FRAME_POINTER_REQUIRED > diff --git a/gcc/testsuite/gcc.target/arm/pr69770.c b/gcc/testsuite/gcc.target/arm/pr69770.c > new file mode 100644 > index 0000000..61e5c6d > --- /dev/null > +++ b/gcc/testsuite/gcc.target/arm/pr69770.c > @@ -0,0 +1,9 @@ > +/* { dg-do compile } */ > +/* { dg-options "-pg -mlong-calls" } */ > + > +extern void g(void); > + > +int f() { g(); return 0; } > + > +/* { dg-final { scan-assembler-not "bl\[ \t\]+__gnu_mcount_nc" } } */ > +/* { dg-final { scan-assembler "__gnu_mcount_nc" } } */ >
From 34993396a43fcfc263db5b02b2d1837c490f52ad Mon Sep 17 00:00:00 2001
From: Charles Baylis <charles.baylis@linaro.org>
Date: Thu, 11 Feb 2016 18:07:00 +0000
Subject: [PATCH] [ARM] PR69770 fix -mlong-calls with -pg
gcc/ChangeLog:
2016-02-12 Charles Baylis <charles.baylis@linaro.org>
* config/arm/arm.c (arm_expand_prologue): Load address of
__gnu_mcount_nc in r12 if profiling and long calls are enabled.
* config/arm/bpabi.h (ARM_FUNCTION_PROFILER): Emit long call to
__gnu_mcount_nc long calls are enabled.
(ARM_FUNCTION_PROFILER_SUPPORTS_LONG_CALLS): New define.
gcc/testsuite/ChangeLog:
2016-02-12 Charles Baylis <charles.baylis@linaro.org>
* gcc.target/arm/pr69770.c: New test.
Change-Id: I4c639a5edf32fa8c67324d37faee1cb4ddd57a5c
diff --git a/gcc/config/arm/arm.c b/gcc/config/arm/arm.c
index 27aecf7..9ce9a58 100644
--- a/gcc/config/arm/arm.c
+++ b/gcc/config/arm/arm.c
@@ -21739,6 +21739,15 @@ arm_expand_prologue (void)
arm_load_pic_register (mask);
}
+ if (crtl->profile && TARGET_LONG_CALLS
+ && ARM_FUNCTION_PROFILER_SUPPORTS_LONG_CALLS)
+ {
+ rtx tmp = gen_rtx_SET (gen_rtx_REG (SImode, IP_REGNUM),
+ gen_rtx_SYMBOL_REF (Pmode, "__gnu_mcount_nc"));
+ emit_insn (tmp);
+ emit_insn (gen_rtx_USE (VOIDmode, gen_rtx_REG (SImode, IP_REGNUM)));
+ }
+
/* If we are profiling, make sure no instructions are scheduled before
the call to mcount. Similarly if the user has requested no
scheduling in the prolog. Similarly if we want non-call exceptions
diff --git a/gcc/config/arm/bpabi.h b/gcc/config/arm/bpabi.h
index 82128ef..b734a24 100644
--- a/gcc/config/arm/bpabi.h
+++ b/gcc/config/arm/bpabi.h
@@ -173,11 +173,21 @@
#undef NO_PROFILE_COUNTERS
#define NO_PROFILE_COUNTERS 1
+#undef ARM_FUNCTION_PROFILER_SUPPORTS_LONG_CALLS
+#define ARM_FUNCTION_PROFILER_SUPPORTS_LONG_CALLS 1
#undef ARM_FUNCTION_PROFILER
#define ARM_FUNCTION_PROFILER(STREAM, LABELNO) \
{ \
- fprintf (STREAM, "\tpush\t{lr}\n"); \
- fprintf (STREAM, "\tbl\t__gnu_mcount_nc\n"); \
+ if (TARGET_LONG_CALLS && TARGET_32BIT) \
+ { \
+ fprintf (STREAM, "\tpush\t{lr}\n"); \
+ /* arm_expand_prolog() has already set up ip to contain the */ \
+ /* address of __gnu_mcount_nc. */ \
+ fprintf (STREAM, "\tblx\tip\n"); \
+ } else { \
+ fprintf (STREAM, "\tpush\t{lr}\n"); \
+ fprintf (STREAM, "\tbl\t__gnu_mcount_nc\n"); \
+ } \
}
#undef SUBTARGET_FRAME_POINTER_REQUIRED
diff --git a/gcc/testsuite/gcc.target/arm/pr69770.c b/gcc/testsuite/gcc.target/arm/pr69770.c
new file mode 100644
index 0000000..61e5c6d
--- /dev/null
+++ b/gcc/testsuite/gcc.target/arm/pr69770.c
@@ -0,0 +1,9 @@
+/* { dg-do compile } */
+/* { dg-options "-pg -mlong-calls" } */
+
+extern void g(void);
+
+int f() { g(); return 0; }
+
+/* { dg-final { scan-assembler-not "bl\[ \t\]+__gnu_mcount_nc" } } */
+/* { dg-final { scan-assembler "__gnu_mcount_nc" } } */
--
1.9.1
When compiling with -mlong-calls and -pg, calls to the __gnu_mcount_nc function are not generated as long calls. This is encountered when building an allyesconfig Linux kernel because the Linux build system generates very large sections by partial linking a large number of object files. This causes link failures, which don't go away with -mlong-calls due to this bug. (However, with this patch linking still fails due to calls in inline asm) For example: extern void g(void); int f() { g(); return 0; } compiles to: push {r4, lr} push {lr} bl __gnu_mcount_nc ;// not a long call ldr r3, .L2 blx r3 ;// a long call to g() mov r0, #0 pop {r4, pc} The call to __gnu_mcount_nc is generated from ARM_FUNCTION_PROFILER in config/arm/bpabi.h. For targets without MOVW/MOVT, the long call sequence requires a load from the literal pool, and it is too late to set up a literal pool entry from within ARM_FUNCTION_PROFILER. My approach to fix this is to modify the prologue generation to load the address of __gnu_mcount_nc into ip, so that it is ready when the call is generated. This patch only implements the fix for ARM and Thumb-2. A similar fix is possible for Thumb-1, but requires more slightly complex changes to the prologue generation to make sure there is a low register available. This feels like a bit of a hack to me, so ideas for a cleaner solution are welcome, if none, is this acceptable for trunk now, or should it wait until GCC 7?