Linker relaxation ignores .option norvc #84
Description
Currently, even if .option norvc is in effect, the assembler still generates relaxable instructions and R_RISCV_RELAX relocations, which may end up getting turned into compressed instructions by the linker anyway:
.section .text
test1:
.option push
.option norvc
lui a0, %hi(data)
addi a0, a0, %lo(data)
.option pop
test2:
1:
.option push
.option norvc
jump 1b, t0
.option pop
.section .rodata
data:
.quad 42If we assemble and link it:
$ riscv64-unknown-linux-gnu-gcc -c -o norvc.o norvc.s
$ riscv64-unknown-linux-gnu-ld -nostdlib -o norvc norvc.o
# This warning is expected
riscv64-unknown-linux-gnu-ld: warning: cannot find entry symbol _start; defaulting to 00000000000100b0
$ riscv64-unknown-linux-gnu-objdump -Mno-aliases -dr norvc
norvc: file format elf64-littleriscv
Disassembly of section .text:
00000000000100b0 <test1>:
100b0: 6541 c.lui a0,0x10
100b2: 0b850513 addi a0,a0,184 # 100b8 <data>
00000000000100b6 <test2>:
100b6: a001 c.j 100b6 <test2>The generated relaxations can be seen in the intermediate object file:
$ riscv64-unknown-linux-gnu-objdump -Mno-aliases -dr norvc.o
norvc.o: file format elf64-littleriscv
Disassembly of section .text:
0000000000000000 <test1>:
0: 00000537 lui a0,0x0
0: R_RISCV_HI20 data
0: R_RISCV_RELAX *ABS*
4: 00050513 addi a0,a0,0 # 0 <test1>
4: R_RISCV_LO12_I data
4: R_RISCV_RELAX *ABS*
0000000000000008 <test2>:
8: 00000297 auipc t0,0x0
8: R_RISCV_CALL .L1^B1
8: R_RISCV_RELAX *ABS*
c: 00028067 jalr zero,0(t0) # 8 <test2>I'm not sure how big of a deal this is. It is certainly unexpected at first glance, but it this even worth doing anything about?
I'm also not sure whether to post it here or post it at https://github.com/riscv-non-isa/riscv-elf-psabi-doc (where linker relaxation is specified), but my idea is that this kind of temporary .option norvc is probably rare enough that this case might not be worth the trouble getting the linker to handle this.