https://sourceware.org/bugzilla/show_bug.cgi?id=32377
Bug ID: 32377
Summary: [RISCV]Variables within the range of gp ± 2KB have not
been indexed
Product: binutils
Version: unspecified
Status: UNCONFIRMED
Severity: normal
Priority: P2
Component: ld
Assignee: unassigned at sourceware dot org
Reporter: mumuxi_ll at outlook dot com
Target Milestone: ---
Hi all,
Here is the test case and ld file：
test.c:
================
int i = 1;
int main(){
return i;
}
================
gp_reloc.ld:
================
MEMORY
{
ROM : ORIGIN = 0x000030000 LENGTH = 0x10000
}
SECTIONS{
.text : {
*(.text)
*(.rodata *.rodata.*)
} >ROM
.data : {
*(.data)
PROVIDE( __global_pointer$ = . + 0x400 );
*(.sdata .sdata.* .sdata*)
*(.gnu.linkonce.s.*)
/* readonly data placed in RAM for access speed */
. = ALIGN(8);
*(.srodata.cst16)
*(.srodata.cst8)
*(.srodata.cst4)
*(.srodata.cst2)
*(.srodata .srodata.*)
*(.sbss*)
} >ROM
PROVIDE( __bss_start = . );
.bss (NOLOAD) : ALIGN(8)
{
*(.sbss*)
*(.gnu.linkonce.sb.*)
*(.bss .bss.*)
*(.gnu.linkonce.b.*)
*(COMMON)
. = ALIGN(4);
} >ROM
PROVIDE( _end = . );
}
================
Perform simple compilation and linking using the following command:
$riscv64-unknown-elf-gcc -march=rv32imac -mabi=ilp32 -c test.c -o test.o
$riscv64-unknown-elf-gcc -march=rv32imac -mabi=ilp32 -o test test.o -T
gp_reloc.ld -Wl,-Map=test.map
$riscv64-unknown-elf-objdump -d test> test.dasm
The disassembly of the main function is as follows, and it can be seen that the
variable i is indexed through the GP register
================
00030082 <main>:
30082: 1141 addi sp,sp,-16
30084: c606 sw ra,12(sp)
30086: c422 sw s0,8(sp)
30088: 0800 addi s0,sp,16
3008a: c041a783 lw a5,-1020(gp) # 31728 <i>
3008e: 853e mv a0,a5
30090: 40b2 lw ra,12(sp)
30092: 4422 lw s0,8(sp)
30094: 0141 addi sp,sp,16
30096: 8082 ret
================
When I change the value of `__globalis_pointer` to . + 0x800, the corresponding
disassembly is as follows:
================
0003008a <main>:
3008a: 1141 addi sp,sp,-16
3008c: c606 sw ra,12(sp)
3008e: c422 sw s0,8(sp)
30090: 0800 addi s0,sp,16
30092: 000317b7 lui a5,0x31
30096: 7507a783 lw a5,1872(a5) # 31750 <i>
3009a: 853e mv a0,a5
3009c: 40b2 lw ra,12(sp)
3009e: 4422 lw s0,8(sp)
300a0: 0141 addi sp,sp,16
300a2: 8082 ret
================
At this point, it becomes indexing the variable i through the `lui+lw`,
however, upon reviewing the map file, it is clear that i falls within the range
of gp ± 2KB
================
0x00031f4c PROVIDE (__global_pointer$ = (. + 0x800))
*(.sdata .sdata.* .sdata*)
.sdata 0x0003174c 0x4 ......
0x0003174c .........
.sdata 0x00031750 0x4 test.o
0x00031750 i
================
So I want to know if this is a bug in ld or if there are additional
restrictions on gp.
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