Re: [PATCH] RISC-V: Use .p2align for code-alignment
On Tue, 15 Nov 2022 at 22:14, Philipp Tomsich wrote: > > Jeff, > > On Tue, 15 Nov 2022 at 17:37, Jeff Law wrote: > > > > > > On 11/13/22 13:41, Philipp Tomsich wrote: > > > > RISC-V's .p2align (currently) ignores the max-skip argument. As we > > have experimental patches underway to address this in a > > backwards-compatible manner, let's prepare GCC for the day when > > binutils gets updated. > > > > gcc/ChangeLog: > > > > * config/riscv/riscv.h (ASM_OUTPUT_MAX_SKIP_ALIGN): Implement. > > > > > > What are the implications if we start using p2align immediately when the > > current (broken?) state of the assembler? I'm pretty sure configure is > > already turning on HAVE_GAS_SKIP_P2ALIGN. From a native risc-v build: > > > > > > auto-host.h:#define HAVE_GAS_MAX_SKIP_P2ALIGN 1 > > This is your tree, which has the (partial fix — i.e., the best we can > do without breaking backward compatibility) for .p2align. > When building against upstream binutils, this should not be defined. After rereading the generated configure-script, I've changed my mind The check the does nothing to ensure that the max-skip is actually honored and only tests whether it is accepted. Having the max-skip silently ignored may still be the lesser evil. Philipp.
Re: [PATCH] RISC-V: Use .p2align for code-alignment
Jeff, On Tue, 15 Nov 2022 at 17:37, Jeff Law wrote: > > > On 11/13/22 13:41, Philipp Tomsich wrote: > > RISC-V's .p2align (currently) ignores the max-skip argument. As we > have experimental patches underway to address this in a > backwards-compatible manner, let's prepare GCC for the day when > binutils gets updated. > > gcc/ChangeLog: > > * config/riscv/riscv.h (ASM_OUTPUT_MAX_SKIP_ALIGN): Implement. > > > What are the implications if we start using p2align immediately when the > current (broken?) state of the assembler? I'm pretty sure configure is > already turning on HAVE_GAS_SKIP_P2ALIGN. From a native risc-v build: > > > auto-host.h:#define HAVE_GAS_MAX_SKIP_P2ALIGN 1 This is your tree, which has the (partial fix — i.e., the best we can do without breaking backward compatibility) for .p2align. When building against upstream binutils, this should not be defined. Philipp.
Re: [PATCH] RISC-V: Use .p2align for code-alignment
On 11/13/22 13:41, Philipp Tomsich wrote: RISC-V's .p2align (currently) ignores the max-skip argument. As we have experimental patches underway to address this in a backwards-compatible manner, let's prepare GCC for the day when binutils gets updated. gcc/ChangeLog: * config/riscv/riscv.h (ASM_OUTPUT_MAX_SKIP_ALIGN): Implement. What are the implications if we start using p2align immediately when the current (broken?) state of the assembler? I'm pretty sure configure is already turning on HAVE_GAS_SKIP_P2ALIGN. From a native risc-v build: auto-host.h:#define HAVE_GAS_MAX_SKIP_P2ALIGN 1 jeff
[PATCH] RISC-V: Use .p2align for code-alignment
RISC-V's .p2align (currently) ignores the max-skip argument. As we
have experimental patches underway to address this in a
backwards-compatible manner, let's prepare GCC for the day when
binutils gets updated.
gcc/ChangeLog:
* config/riscv/riscv.h (ASM_OUTPUT_MAX_SKIP_ALIGN): Implement.
Signed-off-by: Philipp Tomsich
---
gcc/config/riscv/riscv.h | 18 ++
1 file changed, 18 insertions(+)
diff --git a/gcc/config/riscv/riscv.h b/gcc/config/riscv/riscv.h
index 2d0d170645c..c216173cf6b 100644
--- a/gcc/config/riscv/riscv.h
+++ b/gcc/config/riscv/riscv.h
@@ -938,6 +938,24 @@ typedef struct {
fprintf (STREAM, "\t.word\t%sL%d-%sL%d\n", \
LOCAL_LABEL_PREFIX, VALUE, LOCAL_LABEL_PREFIX, REL)
+#ifdef HAVE_GAS_MAX_SKIP_P2ALIGN
+/* Support for -falign-* switches. Use .p2align to ensure that code
+ sections are padded with NOP instructions, rather than zeros. */
+#define ASM_OUTPUT_MAX_SKIP_ALIGN(FILE, LOG, MAX_SKIP) \
+ do \
+{ \
+ if ((LOG) != 0) \
+ { \
+ if ((MAX_SKIP) == 0) \
+ fprintf ((FILE), "\t.p2align %d\n", (int) (LOG)); \
+ else \
+ fprintf ((FILE), "\t.p2align %d,,%d\n", \
+(int) (LOG), (int) (MAX_SKIP));\
+ } \
+} while (0)
+
+#endif /* HAVE_GAS_MAX_SKIP_P2ALIGN */
+
/* This is how to output an assembler line
that says to advance the location counter
to a multiple of 2**LOG bytes. */
--
2.34.1
