bpf: Throw error when external libcalls are generated.
Checks
Commit Message
User-agent: mu4e 1.4.15; emacs 28.1
Author: Cupertino Miranda <cupertino.miranda@oracle.com>
Hi everyone,
The attached patch is a temporary solution for the lack of proper linker
and external library linking of the eBPF platform.
Any calls created by the compiler, that would usually be defined within
libgcc, will endup being undefined in bpftool, when GCC the compiled
code is passed.
This patch anticipates that error to the compiler, by verifiying if
any of those calls are being generated, and reporting as an error.
Looking forward to your comments.
Cheers,
Cupertino
commit c2110ae497c7ff83c309f172bc265973652b760d
This patch enables errors when external calls are created.
When architectural limitations or usage of builtins implies the compiler
to create function calls to external libraries that implement the
functionality, GCC will now report an error claiming that this function
calls are not compatible with eBPF target.
Examples of those are the usage of __builtin_memmove and a sign division
in BPF ISA v3 or below that will require to call __divdi3.
This is currently an eBPF limitation which does not support linking of
object files but rather "raw" non linked ones. Those object files are
loaded and relocated by libbpf and the kernel.
gcc/ChangeLog:
* config/bpf/bpf.cc (bpf_output_call): Report error in case the
function call is for a builtin.
(bpf_external_libcall): Added target hook to detect and report
error when other external calls that are not builtins.
Date: Mon, 27 Nov 2023 14:40:15 +0000
Message-ID: <87o7ffb6pc.fsf@oracle.com>
@@ -744,6 +744,15 @@ bpf_output_call (rtx target)
xops[0] = GEN_INT (TREE_INT_CST_LOW (TREE_VALUE (attr_args)));
output_asm_insn ("call\t%0", xops);
}
+ else if (fndecl_built_in_p (decl))
+ {
+ /* For now lets report this as an error while we are not able to
+ link eBPF object files. In particular with libgcc. */
+ tree name = DECL_NAME (decl);
+ error ("call to external builtin %s in function, which is not supported by "
+ "eBPF", name != NULL_TREE ? IDENTIFIER_POINTER (name) : "(anon)");
+ output_asm_insn ("call 0", NULL);
+ }
else
output_asm_insn ("call\t%0", &target);
@@ -763,6 +772,18 @@ bpf_output_call (rtx target)
return "";
}
+static void
+bpf_external_libcall (rtx fun)
+{
+ tree decl = SYMBOL_REF_DECL (fun);
+ tree name = DECL_NAME (decl);
+ error ("call to external libcall %s in function, which is not supported by "
+ "eBPF", name != NULL_TREE ? IDENTIFIER_POINTER (name) : "(anon)");
+}
+
+#undef TARGET_ASM_EXTERNAL_LIBCALL
+#define TARGET_ASM_EXTERNAL_LIBCALL bpf_external_libcall
+
/* Print register name according to assembly dialect. In normal
syntax registers are printed like %rN where N is the register
number.
@@ -6,7 +6,7 @@ foo (int *p, int *expected, int desired)
{
return __atomic_compare_exchange (p, expected, &desired, 0,
__ATOMIC_ACQUIRE, __ATOMIC_RELAXED);
-}
+} /* { dg-error "call to external builtin" } */
int
foo64 (long *p, long *expected, long desired)
@@ -9,7 +9,7 @@ long
test_atomic_fetch_add (long x)
{
return __atomic_fetch_add (&val, x, __ATOMIC_ACQUIRE);
-}
+} /* { dg-error "call to external builtin" } */
long
test_atomic_fetch_sub (long x)
@@ -20,7 +20,7 @@ void
test_atomic_and (int x)
{
__atomic_and_fetch (&val, x, __ATOMIC_ACQUIRE);
-}
+} /* { dg-error "call to external builtin" } */
void
test_atomic_nand (int x)
@@ -7,7 +7,7 @@ int foo (int *p, int *new)
int old;
__atomic_exchange (p, new, &old, __ATOMIC_RELAXED);
return old;
-}
+} /* { dg-error "call to external builtin" } */
int foo64 (long *p, long *new)
{
@@ -7,6 +7,6 @@ foo ()
{
signed int x = 5;
signed int y = 2;
- signed int z = x / y;
+ signed int z = x / y; /* { dg-error "call to external libcall" } */
}
/* { dg-final { scan-assembler-not "sdiv(32)?\t%r" } } */
@@ -7,6 +7,6 @@ foo ()
{
signed int x = 5;
signed int y = 2;
- signed int z = x % y;
+ signed int z = x % y; /* { dg-error "call to external libcall" } */
}
/* { dg-final { scan-assembler-not "smod(32)?\t%r" } } */