The issue is uncovered by #47698: for IR files without a target triple,
-mtriple= specifies the full target triple while -march= merely sets the
architecture part of the default target triple, leaving a target triple which
may not make sense, e.g. riscv64-apple-darwin.
Therefore, -march= is error-prone and not recommended for tests without a target
triple. The issue has been benign as we recognize $unknown-apple-darwin as ELF instead
of rejecting it outrightly.
This prepares for an upcoming change to make --print-imm-hex the default
behavior of llvm-objdump. These tests were updated in a semi-automatic
fashion.
See D136972 for details.
Currently, the LLVM will print an error like
Unsupported relocation: try to compile with -O2 or above,
or check your static variable usage
if user defines more than one static variables in a single
ELF section (e.g., .bss or .data).
There is ongoing effort to support static and global
variables in libbpf and kernel. This patch removed the
assertion so user programs with static variables won't
fail compilation.
The static variable in-section offset is written to
the "imm" field of the corresponding to-be-relocated
bpf instruction. Below is an example to show how the
application (e.g., libbpf) can relate variable to relocations.
-bash-4.4$ cat g1.c
static volatile long a = 2;
static volatile int b = 3;
int test() { return a + b; }
-bash-4.4$ clang -target bpf -O2 -c g1.c
-bash-4.4$ llvm-readelf -r g1.o
Relocation section '.rel.text' at offset 0x158 contains 2 entries:
Offset Info Type Symbol's Value Symbol's Name
0000000000000000 0000000400000001 R_BPF_64_64 0000000000000000 .data
0000000000000018 0000000400000001 R_BPF_64_64 0000000000000000 .data
-bash-4.4$ llvm-readelf -s g1.o
Symbol table '.symtab' contains 6 entries:
Num: Value Size Type Bind Vis Ndx Name
0: 0000000000000000 0 NOTYPE LOCAL DEFAULT UND
1: 0000000000000000 0 FILE LOCAL DEFAULT ABS g1.c
2: 0000000000000000 8 OBJECT LOCAL DEFAULT 4 a
3: 0000000000000008 4 OBJECT LOCAL DEFAULT 4 b
4: 0000000000000000 0 SECTION LOCAL DEFAULT 4
5: 0000000000000000 64 FUNC GLOBAL DEFAULT 2 test
-bash-4.4$ llvm-objdump -d g1.o
g1.o: file format ELF64-BPF
Disassembly of section .text:
0000000000000000 test:
0: 18 01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 r1 = 0 ll
2: 79 11 00 00 00 00 00 00 r1 = *(u64 *)(r1 + 0)
3: 18 02 00 00 08 00 00 00 00 00 00 00 00 00 00 00 r2 = 8 ll
5: 61 20 00 00 00 00 00 00 r0 = *(u32 *)(r2 + 0)
6: 0f 10 00 00 00 00 00 00 r0 += r1
7: 95 00 00 00 00 00 00 00 exit
-bash-4.4$
. from symbol table, static variable "a" is in section #4, offset 0.
. from symbol table, static variable "b" is in section #4, offset 8.
. the first relocation is against symbol #4:
4: 0000000000000000 0 SECTION LOCAL DEFAULT 4
and in-section offset 0 (see llvm-objdump result)
. the second relocation is against symbol #4:
4: 0000000000000000 0 SECTION LOCAL DEFAULT 4
and in-section offset 8 (see llvm-objdump result)
. therefore, the first relocation is for variable "a", and
the second relocation is for variable "b".
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Yonghong Song <yhs@fb.com>
llvm-svn: 354954
