From a37b5bcf15a682f22ac10d8b7069aa8d115caaef Mon Sep 17 00:00:00 2001 From: Peter Bergner Date: Fri, 6 Nov 2020 17:00:49 -0600 Subject: [PATCH] rs6000: Fix default alignment ABI break caused by MMA base support As part of the MMA base support, we incremented BIGGEST_ALIGNMENT in order to align the __vector_pair and __vector_quad types to 256 and 512 bytes respectively. This had the unintended effect of changing the default alignment used by __attribute__ ((__aligned__)) which causes an ABI break because of some dodgy code in GLIBC's struct pthread. The fix is to revert the BIGGEST_ALIGNMENT change and to force the alignment on the type itself rather than the mode used by the type. 2020-11-06 Peter Bergner gcc/ * config/rs6000/rs6000.h (BIGGEST_ALIGNMENT): Revert previous commit so as not to break the ABI. * config/rs6000/rs6000-call.c (rs6000_init_builtins): Set the ABI mandated alignment for __vector_pair and __vector_quad types. gcc/testsuite/ * gcc.target/powerpc/mma-alignment.c: New test. --- gcc/config/rs6000/rs6000-call.c | 2 ++ gcc/config/rs6000/rs6000.h | 6 ++-- gcc/testsuite/gcc.target/powerpc/mma-alignment.c | 41 ++++++++++++++++++++++++ 3 files changed, 47 insertions(+), 2 deletions(-) create mode 100644 gcc/testsuite/gcc.target/powerpc/mma-alignment.c diff --git a/gcc/config/rs6000/rs6000-call.c b/gcc/config/rs6000/rs6000-call.c index 92378e9..3bd89a7 100644 --- a/gcc/config/rs6000/rs6000-call.c +++ b/gcc/config/rs6000/rs6000-call.c @@ -13191,12 +13191,14 @@ rs6000_init_builtins (void) if (TARGET_EXTRA_BUILTINS) { vector_pair_type_node = make_unsigned_type (256); + SET_TYPE_ALIGN (vector_pair_type_node, 256); SET_TYPE_MODE (vector_pair_type_node, POImode); layout_type (vector_pair_type_node); lang_hooks.types.register_builtin_type (vector_pair_type_node, "__vector_pair"); vector_quad_type_node = make_unsigned_type (512); + SET_TYPE_ALIGN (vector_quad_type_node, 512); SET_TYPE_MODE (vector_quad_type_node, PXImode); layout_type (vector_quad_type_node); lang_hooks.types.register_builtin_type (vector_quad_type_node, diff --git a/gcc/config/rs6000/rs6000.h b/gcc/config/rs6000/rs6000.h index bbd8060..5a47aa1 100644 --- a/gcc/config/rs6000/rs6000.h +++ b/gcc/config/rs6000/rs6000.h @@ -776,8 +776,10 @@ extern unsigned rs6000_pointer_size; /* Allocation boundary (in *bits*) for the code of a function. */ #define FUNCTION_BOUNDARY 32 -/* No data type wants to be aligned rounder than this. */ -#define BIGGEST_ALIGNMENT (TARGET_MMA ? 512 : 128) +/* No data type is required to be aligned rounder than this. Warning, if + BIGGEST_ALIGNMENT is changed, then this may be an ABI break. An example + of where this can break an ABI is in GLIBC's struct _Unwind_Exception. */ +#define BIGGEST_ALIGNMENT 128 /* Alignment of field after `int : 0' in a structure. */ #define EMPTY_FIELD_BOUNDARY 32 diff --git a/gcc/testsuite/gcc.target/powerpc/mma-alignment.c b/gcc/testsuite/gcc.target/powerpc/mma-alignment.c new file mode 100644 index 0000000..0981893 --- /dev/null +++ b/gcc/testsuite/gcc.target/powerpc/mma-alignment.c @@ -0,0 +1,41 @@ +/* { dg-do run } */ +/* { dg-require-effective-target hard_float } */ +/* { dg-options "-O2 -mhard-float" } */ + +#include + +/* The MMA types below are enabled for pre-power10 compiles, because the + built-ins that use them must always be initialized in case the user has + a target attribute or pragma on a function that uses the MMA built-ins. + Since the test below doesn't need any other MMA support, we can enable + this test case on basically any cpu that has hard floating point + registers. */ + +struct +{ + int __attribute__ ((__aligned__)) ivar; + __vector_pair pair; + __vector_quad quad; +} s; + +int +main (void) +{ + /* Verify default alignment is 16-byte aligned (BIGGEST_ALIGNMENT). + This may change in the future, but that is an ABI break, so this + hardcoded test case is here to be a noisy FAIL as a warning, in + case the ABI change was unintended and unwanted. An example of where + this can break an ABI is in glibc's struct _Unwind_Exception. */ + if (__alignof__ (s.ivar) != 16) + abort (); + + /* Verify __vector_pair types are 32-byte aligned. */ + if (__alignof__ (s.pair) != 32) + abort (); + + /* Verify __vector_quad types are 64-byte aligned. */ + if (__alignof__ (s.quad) != 64) + abort (); + + return 0; +} -- 2.7.4