To find out where on-entry register values live at any point in a
program, GDB currently tries to parse to parse the executable code.
This does not work very well, for example it gets confused if some
accesses to the stack use the frame pointer (r31) and some use the
stack pointer (r1). A symptom is that backtraces can be cut short.
This patch enables -fasynchronous-unwind-tables by default for rs6000,
which causes us to emit DWARF unwind tables for all functions, solving
these problems.
This not do anything for sub-targets without DWARF.
It increases executable size, but only modestly, and does not change
memory use, only the disk image.
Various other targets already do this (x86, s390, tile*).
Tested on powerpc64-linux {-m32,-m64}. David, I'd like to commit this
to current trunk; does that seem too dangerous to you?
Segher
2018-04-05 Segher Boessenkool <seg...@kernel.crashing.org>
* common/config/rs6000/rs6000-common.c (rs6000_option_init_struct):
Enable -fasynchronous-unwind-tables by default.
gcc/testsuite/
* gcc.target/powerpc/dfmode_off.c: Add -fno-asynchronous-unwind-tables.
* gcc.target/powerpc/dimode_off.c: Ditto.
* gcc.target/powerpc/tfmode_off.c: Ditto.
* gcc.target/powerpc/timode_off.c: Ditto.
---
gcc/common/config/rs6000/rs6000-common.c | 7 +++++++
gcc/testsuite/gcc.target/powerpc/dfmode_off.c | 2 +-
gcc/testsuite/gcc.target/powerpc/dimode_off.c | 2 +-
gcc/testsuite/gcc.target/powerpc/tfmode_off.c | 2 +-
gcc/testsuite/gcc.target/powerpc/timode_off.c | 2 +-
5 files changed, 11 insertions(+), 4 deletions(-)
diff --git a/gcc/common/config/rs6000/rs6000-common.c
b/gcc/common/config/rs6000/rs6000-common.c
index 0ddadfd..e45ed5e 100644
--- a/gcc/common/config/rs6000/rs6000-common.c
+++ b/gcc/common/config/rs6000/rs6000-common.c
@@ -49,6 +49,13 @@ rs6000_option_init_struct (struct gcc_options *opts)
/* Enable section anchors by default. */
if (!TARGET_MACHO)
opts->x_flag_section_anchors = 1;
+
+ /* By default, always emit DWARF-2 unwind info. This allows debugging
+ without maintaining a stack frame back-chain. It also allows the
+ debugger to find out where on-entry register values are stored at any
+ point in a function, without having to analyze the executable code (which
+ isn't even possible to do in the general case). */
+ opts->x_flag_asynchronous_unwind_tables = 1;
}
/* Implement TARGET_OPTION_DEFAULT_PARAMS. */
diff --git a/gcc/testsuite/gcc.target/powerpc/dfmode_off.c
b/gcc/testsuite/gcc.target/powerpc/dfmode_off.c
index 1942f48..b5940cb 100644
--- a/gcc/testsuite/gcc.target/powerpc/dfmode_off.c
+++ b/gcc/testsuite/gcc.target/powerpc/dfmode_off.c
@@ -1,5 +1,5 @@
/* { dg-do assemble } */
-/* { dg-options "-O2 -fno-align-functions -mtraceback=no -save-temps" } */
+/* { dg-options "-O2 -fno-align-functions -fno-asynchronous-unwind-tables
-mtraceback=no -save-temps" } */
void w1 (void *x, double y) { *(double *) (x + 32767) = y; }
void w2 (void *x, double y) { *(double *) (x + 32766) = y; }
diff --git a/gcc/testsuite/gcc.target/powerpc/dimode_off.c
b/gcc/testsuite/gcc.target/powerpc/dimode_off.c
index 77a1863..19ca40c 100644
--- a/gcc/testsuite/gcc.target/powerpc/dimode_off.c
+++ b/gcc/testsuite/gcc.target/powerpc/dimode_off.c
@@ -1,5 +1,5 @@
/* { dg-do assemble } */
-/* { dg-options "-O2 -fno-align-functions -mtraceback=no -save-temps" } */
+/* { dg-options "-O2 -fno-align-functions -fno-asynchronous-unwind-tables
-mtraceback=no -save-temps" } */
void w1 (void *x, long long y) { *(long long *) (x + 32767) = y; }
void w2 (void *x, long long y) { *(long long *) (x + 32766) = y; }
diff --git a/gcc/testsuite/gcc.target/powerpc/tfmode_off.c
b/gcc/testsuite/gcc.target/powerpc/tfmode_off.c
index cbb3d75..f19e759 100644
--- a/gcc/testsuite/gcc.target/powerpc/tfmode_off.c
+++ b/gcc/testsuite/gcc.target/powerpc/tfmode_off.c
@@ -2,7 +2,7 @@
/* { dg-skip-if "" { powerpc-ibm-aix* } } */
/* { dg-skip-if "no TFmode" { powerpc-*-eabi* } } */
/* { dg-require-effective-target longdouble128 } */
-/* { dg-options "-O2 -fno-align-functions -mtraceback=no -save-temps" } */
+/* { dg-options "-O2 -fno-align-functions -fno-asynchronous-unwind-tables
-mtraceback=no -save-temps" } */
typedef float TFmode __attribute__ ((mode (TF)));
diff --git a/gcc/testsuite/gcc.target/powerpc/timode_off.c
b/gcc/testsuite/gcc.target/powerpc/timode_off.c
index efeffa7..b635953 100644
--- a/gcc/testsuite/gcc.target/powerpc/timode_off.c
+++ b/gcc/testsuite/gcc.target/powerpc/timode_off.c
@@ -1,6 +1,6 @@
/* { dg-do assemble { target { lp64 } } } */
/* { dg-skip-if "do not override -mcpu" { powerpc*-*-* } { "-mcpu=*" } {
"-mcpu=power5" } } */
-/* { dg-options "-O2 -fno-align-functions -mtraceback=no -save-temps
-mcpu=power5" } */
+/* { dg-options "-O2 -fno-align-functions -fno-asynchronous-unwind-tables
-mtraceback=no -save-temps -mcpu=power5" } */
typedef int TImode __attribute__ ((mode (TI)));
--
1.8.3.1
