Re: [PATCH] Use SHF_GNU_RETAIN to preserve symbol definitions

[Jozef Lawrynowicz]

On Thu, Nov 12, 2020 at 02:41:52PM -0800, H.J. Lu wrote:
> diff --git a/gcc/varasm.c b/gcc/varasm.c
> index 435c7b348a5..c48ef9692ee 100644
> --- a/gcc/varasm.c
> +++ b/gcc/varasm.c
> @@ -289,6 +289,10 @@ get_section (const char *name, unsigned int flags, tree 
> decl,
>    slot = section_htab->find_slot_with_hash (name, htab_hash_string (name),
>                                           INSERT);
>    flags |= SECTION_NAMED;
> +#if HAVE_GAS_SHF_GNU_RETAIN
> +  if (decl != nullptr && DECL_PRESERVE_P (decl))

Minor nit, but I think this should be "decl != NULL_TREE".

We should also test that "used" with the "section" attribute applies the
"R" flag. Please apply the attached patch if this gets approved. These
new tests pass with arm-none-eabi and x86_64-pc-linux-gnu.

Thanks,
Jozef

commit cf8e26deb43d13268ab6ee231995aecbf41ba3a3
Author: Jozef Lawrynowicz <joze...@mittosystems.com>
Date:   Fri Nov 13 11:07:14 2020 +0000

    Test "used" attribute in conjunction "section" attribute

diff --git a/gcc/testsuite/gcc.c-torture/compile/attr-used-retain-1.c 
b/gcc/testsuite/gcc.c-torture/compile/attr-used-retain-1.c
index b7763af11e4..5f6cbca6e33 100644
--- a/gcc/testsuite/gcc.c-torture/compile/attr-used-retain-1.c
+++ b/gcc/testsuite/gcc.c-torture/compile/attr-used-retain-1.c
@@ -4,6 +4,7 @@
 /* { dg-final { scan-assembler ".bss.*,\"awR\"" } } */
 /* { dg-final { scan-assembler ".data.*,\"awR\"" } } */
 /* { dg-final { scan-assembler ".rodata.*,\"aR\"" } } */
+/* { dg-final { scan-assembler ".data.used_foo_sec,\"awR\"" } } */
 
 void __attribute__((used)) used_fn (void) { }
 void unused_fn (void) { }
@@ -30,3 +31,5 @@ int __attribute__((used)) used_data2 = 1;
 const int __attribute__((used)) used_rodata2 = 2;
 int __attribute__((used)) used_comm2;
 static int __attribute__((used)) used_lcomm2;
+
+int __attribute__((used,section(".data.used_foo_sec"))) used_foo = 2;
diff --git a/gcc/testsuite/gcc.c-torture/compile/attr-used-retain-2.c 
b/gcc/testsuite/gcc.c-torture/compile/attr-used-retain-2.c
index e3b3cf184f8..be5f3917ac8 100644
--- a/gcc/testsuite/gcc.c-torture/compile/attr-used-retain-2.c
+++ b/gcc/testsuite/gcc.c-torture/compile/attr-used-retain-2.c
@@ -10,6 +10,7 @@
 /* { dg-final { scan-assembler ".rodata.used_rodata2,\"aR\"" } } */
 /* { dg-final { scan-assembler ".bss.used_lcomm,\"awR\"" { target arm-*-* } } 
} */
 /* { dg-final { scan-assembler ".bss.used_lcomm2,\"awR\"" { target arm-*-* } } 
} */
+/* { dg-final { scan-assembler ".data.used_foo_sec,\"awR\"" } } */
 /* { dg-options "-ffunction-sections -fdata-sections" } */
 
 #include "attr-used-retain-1.c"