* [RS6000] Power10 libffi fixes
@ 2020-09-22 0:30 Alan Modra
2020-09-23 0:16 ` Segher Boessenkool
0 siblings, 1 reply; 4+ messages in thread
From: Alan Modra @ 2020-09-22 0:30 UTC (permalink / raw)
To: gcc-patches; +Cc: Segher Boessenkool
Power10 pc-relative code doesn't use or preserve r2 as a TOC pointer.
That means calling between pc-relative and TOC using code can't be
done without intervening linker stubs, and a call from TOC code to
pc-relative code must have a nop after the bl in order to restore r2.
Now the PowerPC libffi assembly code doesn't use r2 except for the
implicit use when making calls back to C, ffi_closure_helper_LINUX64
and ffi_prep_args64. So changing the assembly to interoperate with
pc-relative code without stubs is easily done. Controlling that is a
new built-in macro.
Upstream libffi currently has a different patch applied to work around
the power10 build failure. I'll post a delta for upstream.
Bootstrapped and regression tested on power8, built for power10.
gcc/
* config/rs6000/rs6000-c.c (rs6000_target_modify_macros):
Conditionally define __PCREL__.
libffi/
* src/powerpc/linux64.S (ffi_call_LINUX64): Don't emit global
entry when __PCREL__. Call using @notoc.
(ffi_closure_LINUX64, ffi_go_closure_linux64): Likewise.
diff --git a/gcc/config/rs6000/rs6000-c.c b/gcc/config/rs6000/rs6000-c.c
index f5982907e90..cc1e997524e 100644
--- a/gcc/config/rs6000/rs6000-c.c
+++ b/gcc/config/rs6000/rs6000-c.c
@@ -597,6 +597,9 @@ rs6000_target_modify_macros (bool define_p, HOST_WIDE_INT flags,
/* Tell the user if we support the MMA instructions. */
if ((flags & OPTION_MASK_MMA) != 0)
rs6000_define_or_undefine_macro (define_p, "__MMA__");
+ /* Whether pc-relative code is being generated. */
+ if ((flags & OPTION_MASK_PCREL) != 0)
+ rs6000_define_or_undefine_macro (define_p, "__PCREL__");
}
void
diff --git a/libffi/src/powerpc/linux64.S b/libffi/src/powerpc/linux64.S
index b2ae60ead6e..bfb4d2957ae 100644
--- a/libffi/src/powerpc/linux64.S
+++ b/libffi/src/powerpc/linux64.S
@@ -36,8 +36,10 @@
.cfi_startproc
# if _CALL_ELF == 2
ffi_call_LINUX64:
+# ifndef __PCREL__
addis %r2, %r12, .TOC.-ffi_call_LINUX64@ha
addi %r2, %r2, .TOC.-ffi_call_LINUX64@l
+# endif
.localentry ffi_call_LINUX64, . - ffi_call_LINUX64
# else
.section ".opd","aw"
@@ -89,7 +91,11 @@ ffi_call_LINUX64:
/* Call ffi_prep_args64. */
mr %r4, %r1
# if defined _CALL_LINUX || _CALL_ELF == 2
+# ifdef __PCREL__
+ bl ffi_prep_args64@notoc
+# else
bl ffi_prep_args64
+# endif
# else
bl .ffi_prep_args64
# endif
diff --git a/libffi/src/powerpc/linux64_closure.S b/libffi/src/powerpc/linux64_closure.S
index 6487d2a2970..938e86034f1 100644
--- a/libffi/src/powerpc/linux64_closure.S
+++ b/libffi/src/powerpc/linux64_closure.S
@@ -37,8 +37,10 @@
.cfi_startproc
# if _CALL_ELF == 2
ffi_closure_LINUX64:
+# ifndef __PCREL__
addis %r2, %r12, .TOC.-ffi_closure_LINUX64@ha
addi %r2, %r2, .TOC.-ffi_closure_LINUX64@l
+# endif
.localentry ffi_closure_LINUX64, . - ffi_closure_LINUX64
# else
.section ".opd","aw"
@@ -155,7 +157,11 @@ ffi_closure_LINUX64:
# make the call
# if defined _CALL_LINUX || _CALL_ELF == 2
+# ifdef __PCREL__
+ bl ffi_closure_helper_LINUX64@notoc
+# else
bl ffi_closure_helper_LINUX64
+# endif
# else
bl .ffi_closure_helper_LINUX64
# endif
@@ -396,8 +402,10 @@ ffi_closure_LINUX64:
.cfi_startproc
# if _CALL_ELF == 2
ffi_go_closure_linux64:
+# ifndef __PCREL__
addis %r2, %r12, .TOC.-ffi_go_closure_linux64@ha
addi %r2, %r2, .TOC.-ffi_go_closure_linux64@l
+# endif
.localentry ffi_go_closure_linux64, . - ffi_go_closure_linux64
# else
.section ".opd","aw"
--
Alan Modra
Australia Development Lab, IBM
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [RS6000] Power10 libffi fixes
2020-09-22 0:30 [RS6000] Power10 libffi fixes Alan Modra
@ 2020-09-23 0:16 ` Segher Boessenkool
2020-09-24 3:41 ` Alan Modra
0 siblings, 1 reply; 4+ messages in thread
From: Segher Boessenkool @ 2020-09-23 0:16 UTC (permalink / raw)
To: Alan Modra; +Cc: gcc-patches
Hi!
On Tue, Sep 22, 2020 at 10:00:11AM +0930, Alan Modra wrote:
> Power10 pc-relative code doesn't use or preserve r2 as a TOC pointer.
> That means calling between pc-relative and TOC using code can't be
> done without intervening linker stubs, and a call from TOC code to
> pc-relative code must have a nop after the bl in order to restore r2.
>
> Now the PowerPC libffi assembly code doesn't use r2 except for the
> implicit use when making calls back to C, ffi_closure_helper_LINUX64
> and ffi_prep_args64. So changing the assembly to interoperate with
> pc-relative code without stubs is easily done. Controlling that is a
> new built-in macro.
>
> Upstream libffi currently has a different patch applied to work around
> the power10 build failure. I'll post a delta for upstream.
> Bootstrapped and regression tested on power8, built for power10.
>
> gcc/
> * config/rs6000/rs6000-c.c (rs6000_target_modify_macros):
> Conditionally define __PCREL__.
Please do that as a separate (earlier) patch (because it *is*, and to
simplify backports, etc).
> libffi/
> * src/powerpc/linux64.S (ffi_call_LINUX64): Don't emit global
> entry when __PCREL__. Call using @notoc.
> (ffi_closure_LINUX64, ffi_go_closure_linux64): Likewise.
This is okay for trunk, and for backports (possibly expedited, talk
with Peter for what is wanted/needed for AT).
Thanks!
Segher
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [RS6000] Power10 libffi fixes
2020-09-23 0:16 ` Segher Boessenkool
@ 2020-09-24 3:41 ` Alan Modra
2020-09-24 5:39 ` Alan Modra
0 siblings, 1 reply; 4+ messages in thread
From: Alan Modra @ 2020-09-24 3:41 UTC (permalink / raw)
To: Segher Boessenkool; +Cc: gcc-patches
On Tue, Sep 22, 2020 at 07:16:57PM -0500, Segher Boessenkool wrote:
> Hi!
>
> On Tue, Sep 22, 2020 at 10:00:11AM +0930, Alan Modra wrote:
> > gcc/
> > * config/rs6000/rs6000-c.c (rs6000_target_modify_macros):
> > Conditionally define __PCREL__.
>
> Please do that as a separate (earlier) patch (because it *is*, and to
> simplify backports, etc).
Done.
> > libffi/
> > * src/powerpc/linux64.S (ffi_call_LINUX64): Don't emit global
> > entry when __PCREL__. Call using @notoc.
> > (ffi_closure_LINUX64, ffi_go_closure_linux64): Likewise.
>
> This is okay for trunk, and for backports (possibly expedited, talk
> with Peter for what is wanted/needed for AT).
I've fixed the changelog, a comment, and added a nop after bl for the
old calls without @notoc. While there really isn't a need for the
nops in libffi.so since the callee is hidden visibility, there is a
miniscule chance that a static libffi.a user has a very large TOC and
somehow manages to have ffi_call_LINUX64 and ffi_prep_args64 using
different TOC pointers. In that case the linker would arrange the
call to go via a toc-adjusting stub and want to replace the nop with a
toc restore.
--
Alan Modra
Australia Development Lab, IBM
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [RS6000] Power10 libffi fixes
2020-09-24 3:41 ` Alan Modra
@ 2020-09-24 5:39 ` Alan Modra
0 siblings, 0 replies; 4+ messages in thread
From: Alan Modra @ 2020-09-24 5:39 UTC (permalink / raw)
To: Segher Boessenkool; +Cc: gcc-patches
On Thu, Sep 24, 2020 at 01:11:02PM +0930, Alan Modra wrote:
> I've fixed the changelog, a comment, and added a nop after bl for the
> old calls without @notoc. While there really isn't a need for the
> nops in libffi.so since the callee is hidden visibility, there is a
> miniscule chance that a static libffi.a user has a very large TOC and
> somehow manages to have ffi_call_LINUX64 and ffi_prep_args64 using
> different TOC pointers. In that case the linker would arrange the
> call to go via a toc-adjusting stub and want to replace the nop with a
> toc restore.
Adding those nops broke libffi, and I pushed the patch before
bootstrap finished.. So this one committed as obvious to fix the
breakage.
* src/powerpc/linux64_closure.S (ffi_closure_LINUX64): Correct
location of .Lret.
diff --git a/libffi/src/powerpc/linux64_closure.S b/libffi/src/powerpc/linux64_closure.S
index 3e30db36190..5663bb40223 100644
--- a/libffi/src/powerpc/linux64_closure.S
+++ b/libffi/src/powerpc/linux64_closure.S
@@ -159,15 +159,17 @@ ffi_closure_LINUX64:
# if defined _CALL_LINUX || _CALL_ELF == 2
# ifdef __PCREL__
bl ffi_closure_helper_LINUX64@notoc
+.Lret:
# else
bl ffi_closure_helper_LINUX64
+.Lret:
nop
# endif
# else
bl .ffi_closure_helper_LINUX64
+.Lret:
nop
# endif
-.Lret:
# now r3 contains the return type
# so use it to look up in a table
--
Alan Modra
Australia Development Lab, IBM
^ permalink raw reply [flat|nested] 4+ messages in thread
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2020-09-22 0:30 [RS6000] Power10 libffi fixes Alan Modra
2020-09-23 0:16 ` Segher Boessenkool
2020-09-24 3:41 ` Alan Modra
2020-09-24 5:39 ` Alan Modra
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