core/cortex-m0: fix vecttable.c when compiling with clang

This is the same as commit 0907090490b07357902927f089228d63a775cdf0,
which made the same change for core/cortex-m/vecttable.c.

The vecttable section was attempting to add the "a" flag, which
indicates the section is allocatable:
https://sourceware.org/binutils/docs/as/Section.html.

Comparing the "text.vecttable" ELF section headers for gcc before and
after this change, in both cases the ALLOC flag is set and there are no
other difference in flags:

arm-none-eabi-objdump -h \
	build/discovery-stm32f072/RO/core/cortex-m0/vecttable.o

Sections:
Idx Name          Size      VMA       LMA       File off  Algn
  ...
  4 .text.vecttable 000000c0  00000000  00000000  0000003c  2**2
                  CONTENTS, ALLOC, LOAD, RELOC, READONLY, CODE
  ...

However, if we examine the clang section headers before this change we
see that before the change the section name is .text.vecttable,"a",
rather than .text.vecttable:

arm-none-eabi-objdump -h \
	build/discovery-stm32f072/RO/core/cortex-m0/vecttable.o

Sections:
Idx Name          Size      VMA       LMA       File off  Algn
  ...
  3 .text.vecttable,"a" @ 000000c0  00000000  00000000  00000044  2**2
                  CONTENTS, ALLOC, LOAD, RELOC, DATA
  ...

After the change, the section is correctly named .text.vecttable:

Sections:
Idx Name          Size      VMA       LMA       File off  Algn
  ...
  3 .text.vecttable 000000c0  00000000  00000000  00000044  2**2
                  CONTENTS, ALLOC, LOAD, RELOC, READONLY, DATA
  ...

We also see that the ALLOC flag is correctly set.

BRANCH=none
BUG=b:172020503
TEST=./util/compare_build.sh -b all -j 120
     => MATCH

Signed-off-by: Tom Hughes <tomhughes@chromium.org>
Change-Id: I8d84f44266fe3bfe3a942401d9fdbe7760c6af53
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/3253650
Reviewed-by: Denis Brockus <dbrockus@chromium.org>

1 files changed, 6 insertions, 2 deletions

diff --git a/core/cortex-m0/vecttable.c b/core/cortex-m0/vecttable.c
index de667749ad..5c69f6d6c8 100644
--- a/core/cortex-m0/vecttable.c
+++ b/core/cortex-m0/vecttable.c
@@ -77,7 +77,11 @@ extern void reset(void);
 #pragma clang diagnostic ignored "-Winitializer-overrides"
 #endif /* __clang__ */
 
-#define table(x) func vectors[] __attribute__((section(".text.vecttable,\"a\" @"))) = { x[IRQ_UNUSED_OFFSET] = null };
+#define table(x)							     \
+	const func vectors[] __attribute__((section(".text.vecttable"))) = { \
+		x							     \
+		[IRQ_UNUSED_OFFSET] = null				     \
+	}
 
 #define vec(name) name ## _handler,
 #define irq(num) [num < CONFIG_IRQ_COUNT ? num + IRQ_OFFSET : IRQ_UNUSED_OFFSET] = vec(irq_ ## num)
@@ -135,7 +139,7 @@ table(
 	irq(29)
 	irq(30)
 	irq(31)
-)
+);
 
 #if PASS == 2
 #ifdef __clang__