[Bug ld/24992] New: RISC-V: partial relaxing against global pointer with sdata section alignment

[yitingwang16 at outlook dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=24992

            Bug ID: 24992
           Summary: RISC-V: partial relaxing against global pointer with
                    sdata section alignment
           Product: binutils
           Version: 2.30
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: ld
          Assignee: unassigned at sourceware dot org
          Reporter: yitingwang16 at outlook dot com
  Target Milestone: ---

A simple test case below to trigger the weird behavior of GP linker relaxation:
$ cat test.c
char __attribute__ ((aligned(2))) x = 'x';
char a = 1;
char b = 2;
char c = 3;
char d = 4;
char e = 5;

int main()
{
    return a + b + c + d + e;
}

$ riscv64-unknown-linux-gnu-gcc -nostdlib -o test test.c

HI20/LO12 relocations that reference c, d and e are relaxed against gp:
$ riscv64-unknown-linux-gnu-objdump -D test

00000000000100e8 <main>:
   100e8:       1141                    addi    sp,sp,-16
   100ea:       e422                    sd      s0,8(sp)
   100ec:       0800                    addi    s0,sp,16
   100ee:       67c5                    lui     a5,0x11
   100f0:       1317c783                lbu     a5,305(a5) # 11131 <a>
   100f4:       0007871b                sext.w  a4,a5
   100f8:       67c5                    lui     a5,0x11
   100fa:       1327c783                lbu     a5,306(a5) # 11132 <b>
   100fe:       2781                    sext.w  a5,a5
   10100:       9fb9                    addw    a5,a5,a4
   10102:       0007871b                sext.w  a4,a5
   10106:       8031c783                lbu     a5,-2045(gp) # 11133 <c>
   1010a:       2781                    sext.w  a5,a5
   1010c:       9fb9                    addw    a5,a5,a4
   1010e:       0007871b                sext.w  a4,a5
   10112:       8041c783                lbu     a5,-2044(gp) # 11134 <d>
   10116:       2781                    sext.w  a5,a5
   10118:       9fb9                    addw    a5,a5,a4
   1011a:       0007871b                sext.w  a4,a5
   1011e:       8051c783                lbu     a5,-2043(gp) # 11135 <e>
   10122:       2781                    sext.w  a5,a5
   10124:       9fb9                    addw    a5,a5,a4
   10126:       2781                    sext.w  a5,a5
   10128:       853e                    mv      a0,a5
   1012a:       6422                    ld      s0,8(sp)
   1012c:       0141                    addi    sp,sp,16
   1012e:       8082                    ret

Change test.c line#1 to:
char __attribute__ ((aligned(4))) x = 'x';

Only HI20/LO12 relocation that references e is relaxed against gp:
$ riscv64-unknown-linux-gnu-objdump -D test
00000000000100e8 <main>:
   100e8:       1141                    addi    sp,sp,-16
   100ea:       e422                    sd      s0,8(sp)
   100ec:       0800                    addi    s0,sp,16
   100ee:       67c5                    lui     a5,0x11
   100f0:       1357c783                lbu     a5,309(a5) # 11135 <a>
   100f4:       0007871b                sext.w  a4,a5
   100f8:       67c5                    lui     a5,0x11
   100fa:       1367c783                lbu     a5,310(a5) # 11136 <b>
   100fe:       2781                    sext.w  a5,a5
   10100:       9fb9                    addw    a5,a5,a4
   10102:       0007871b                sext.w  a4,a5
   10106:       67c5                    lui     a5,0x11
   10108:       1377c783                lbu     a5,311(a5) # 11137 <c>
   1010c:       2781                    sext.w  a5,a5
   1010e:       9fb9                    addw    a5,a5,a4
   10110:       0007871b                sext.w  a4,a5
   10114:       67c5                    lui     a5,0x11
   10116:       1387c783                lbu     a5,312(a5) # 11138 <d>
   1011a:       2781                    sext.w  a5,a5
   1011c:       9fb9                    addw    a5,a5,a4
   1011e:       0007871b                sext.w  a4,a5
   10122:       8051c783                lbu     a5,-2043(gp) # 11139 <e>
   10126:       2781                    sext.w  a5,a5
   10128:       9fb9                    addw    a5,a5,a4
   1012a:       2781                    sext.w  a5,a5
   1012c:       853e                    mv      a0,a5
   1012e:       6422                    ld      s0,8(sp)
   10130:       0141                    addi    sp,sp,16
   10132:       8082                    ret

Change test.c line#1 to:
char __attribute__ ((aligned(8))) x = 'x';

Then there is no relaxation against gp.

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