[gcc r10-9762] bpf: allow BSS symbols to be global symbols

[gcc r10-9762] bpf: allow BSS symbols to be global symbols

[David Faust]

https://gcc.gnu.org/g:cc2416801e07b4f6950b4a7d374e57329999bc74

commit r10-9762-gcc2416801e07b4f6950b4a7d374e57329999bc74
Author: YiFei Zhu <zhuyifei1999@gmail.com>
Date:   Thu Apr 22 05:05:57 2021 -0500

    bpf: allow BSS symbols to be global symbols
    
    Prior to this, a BSS declaration such as:
    
      int foo;
      static int bar;
    
    Generates:
    
      .global foo
      .local  foo
      .comm   foo,4,4
      .local  bar
      .comm   bar,4,4
    
    Creating symbols:
    
      0000000000000000 b foo
      0000000000000004 b bar
    
    Both symbols are local. However, libbpf bpf_object__variable_offset
    rquires symbols to be STB_GLOBAL & STT_OBJECT for data section lookup.
    This patch makes the same declaration generate:
    
      .global foo
      .type   foo, @object
      .lcomm  foo,4,4
      .local  bar
      .comm   bar,4,4
    
    Creating symbols:
    
      0000000000000000 B foo
      0000000000000004 b bar
    
    And libbpf will be okay with looking up the global symbol "foo".
    
    2021-04-22  YiFei Zhu  <zhuyifei1999@gmail.com>
    
    gcc/
    
            * config/bpf/bpf.h (ASM_OUTPUT_ALIGNED_BSS): Use .type and .lcomm.
    
    (cherry picked from commit 886b6c1e8af502b69e3f318b9830b73b88215878)

Diff:
---
 gcc/config/bpf/bpf.h | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/gcc/config/bpf/bpf.h b/gcc/config/bpf/bpf.h
index 01e30b7e60e..88183e69564 100644
--- a/gcc/config/bpf/bpf.h
+++ b/gcc/config/bpf/bpf.h
@@ -422,9 +422,15 @@ enum reg_class
    Try to use asm_output_aligned_bss to implement this macro.  */
 
 #define ASM_OUTPUT_ALIGNED_BSS(FILE, DECL, NAME, SIZE, ALIGN)	\
-  do {								\
-    ASM_OUTPUT_ALIGNED_LOCAL (FILE, NAME, SIZE, ALIGN);		\
-  } while (0)
+  do									\
+    {									\
+      ASM_OUTPUT_TYPE_DIRECTIVE (FILE, NAME, "object");			\
+      fprintf ((FILE), "%s", "\t.lcomm\t");				\
+      assemble_name ((FILE), (NAME));					\
+      fprintf ((FILE), "," HOST_WIDE_INT_PRINT_UNSIGNED ",%u\n",	\
+	       (SIZE), (ALIGN) / BITS_PER_UNIT);			\
+    }									\
+  while (0)
 
 /*** Output and Generation of Labels.  */