This patch fixes the BPF backend to not generate `exit' (return) instructions in epilogues of functions that are declared as naked via the corresponding compiler attribute. Having extra exit instructions upsets the kernel BPF verifier.
Tested in bpf-unknown-none target in x86_64-linux-gnu host. gcc/ChangeLog * config/bpf/bpf.cc (bpf_expand_epilogue): Do not emit a return instruction in naked function epilogues. gcc/testsuite/ChangeLog * gcc.target/bpf/naked-1.c: Update test to not expect an exit instruction in naked function. * gcc.target/bpf/naked-2.c: New test. --- gcc/config/bpf/bpf.cc | 5 ++--- gcc/testsuite/gcc.target/bpf/naked-1.c | 1 - gcc/testsuite/gcc.target/bpf/naked-2.c | 10 ++++++++++ 3 files changed, 12 insertions(+), 4 deletions(-) create mode 100644 gcc/testsuite/gcc.target/bpf/naked-2.c diff --git a/gcc/config/bpf/bpf.cc b/gcc/config/bpf/bpf.cc index 9af1728d852..d6ca47eeecb 100644 --- a/gcc/config/bpf/bpf.cc +++ b/gcc/config/bpf/bpf.cc @@ -420,9 +420,8 @@ bpf_expand_epilogue (void) /* See note in bpf_expand_prologue for an explanation on why we are not restoring callee-saved registers in BPF. */ - /* If we ever need to do anything else than just generating a return - instruction here, please mind the `naked' function attribute. */ - + if (lookup_attribute ("naked", DECL_ATTRIBUTES (cfun->decl)) != NULL_TREE) + return; emit_jump_insn (gen_exit ()); } diff --git a/gcc/testsuite/gcc.target/bpf/naked-1.c b/gcc/testsuite/gcc.target/bpf/naked-1.c index cbbc4c51697..dc8ac2619cc 100644 --- a/gcc/testsuite/gcc.target/bpf/naked-1.c +++ b/gcc/testsuite/gcc.target/bpf/naked-1.c @@ -9,4 +9,3 @@ int __attribute__((naked)) foo() __asm__ volatile ("@ naked"); } /* { dg-final { scan-assembler "\t@ naked" } } */ -/* { dg-final { scan-assembler "\texit\n" } } */ diff --git a/gcc/testsuite/gcc.target/bpf/naked-2.c b/gcc/testsuite/gcc.target/bpf/naked-2.c new file mode 100644 index 00000000000..25aebf84755 --- /dev/null +++ b/gcc/testsuite/gcc.target/bpf/naked-2.c @@ -0,0 +1,10 @@ +/* Verify that __attribute__((naked)) produces functions without implicit + `exit' instructions in the epilogue. */ +/* { dg-do compile } */ +/* { dg-options "-O0" } */ + +int __attribute__((naked)) foo() +{ + __asm__ volatile ("exit"); +} +/* { dg-final { scan-assembler-times "\texit" 1 } } */ -- 2.30.2