https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82717
Bug ID: 82717
Summary: [RISCV] Default value of the -mabi option doesn't
match documentation
Product: gcc
Version: 8.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: asb at lowrisc dot org
Target Milestone: ---
The documentation for the -mabi command-line option for RISC-V states:
"""
@item -mabi=@var{ABI-string}
@opindex mabi
Specify integer and floating-point calling convention. This defaults to the
natural calling convention: e.g.@ LP64 for RV64I, ILP32 for RV32I, LP64D for
RV64G.
"""
By my reading, this indicates that -march=rv32imafd would imply -mabi=ilp32d as
the "natural" calling convention. This is not the case. Note how the soft-float
calling convention is used in the example below:
$ cat t.c
double callee(float a, double b, int c) {
return a+b+c;
}
double caller(void) {
callee(1.0, 2.0, 3);
}
$ ./riscv32-unknown-elf-gcc -march=rv32imafdc t.c -c -S -o -
.file "t.c"
.option nopic
.text
.align 1
.globl callee
.type callee, @function
callee:
add sp,sp,-48
sw s0,44(sp)
add s0,sp,48
sw a0,-20(s0)
sw a1,-32(s0)
sw a2,-28(s0)
sw a3,-24(s0)
flw fa5,-20(s0)
fcvt.d.s fa4,fa5
fld fa5,-32(s0)
fadd.d fa4,fa4,fa5
lw a5,-24(s0)
fcvt.d.w fa5,a5
fadd.d fa5,fa4,fa5
fsd fa5,-40(s0)
lw a0,-40(s0)
lw a1,-36(s0)
lw s0,44(sp)
add sp,sp,48
jr ra
.size callee, .-callee
.align 1
.globl caller
.type caller, @function
caller:
add sp,sp,-32
sw ra,28(sp)
sw s0,24(sp)
add s0,sp,32
lui a5,%hi(.LC0)
addi a5,a5,%lo(.LC0)
fld fa4,0(a5)
lui a5,%hi(.LC1)
flw fa5,%lo(.LC1)(a5)
li a3,3
fsd fa4,-24(s0)
lw a1,-24(s0)
lw a2,-20(s0)
fmv.x.s a0,fa5
call callee
nop
fsd fa5,-24(s0)
lw a0,-24(s0)
lw a1,-20(s0)
lw ra,28(sp)
lw s0,24(sp)
add sp,sp,32
jr ra
.size caller, .-caller
.section .rodata
.align 3
.LC0:
.word 0
.word 1073741824
.align 2
.LC1:
.word 1065353216
.ident "GCC: (GNU) 8.0.0 20171025 (experimental)"
I would also note that the documentation could be improved by better detailing
the accepted ABI strings and giving valid examples (ILP32 isn't accepted as it
is uppercase).
