selftests/bpf: fix uprobe offset calculation in selftests

Fix how selftests determine relative offset of a function that is
uprobed. Previously, there was an assumption that uprobed function is
always in the first executable region, which is not always the case
(libbpf CI hits this case now). So get_base_addr() approach in isolation
doesn't work anymore. So teach get_uprobe_offset() to determine correct
memory mapping and calculate uprobe offset correctly.

While at it, I merged together two implementations of
get_uprobe_offset() helper, moving powerpc64-specific logic inside (had
to add extra {} block to avoid unused variable error for insn).

Also ensured that uprobed functions are never inlined, but are still
static (and thus local to each selftest), by using a no-op asm volatile
block internally. I didn't want to keep them global __weak, because some
tests use uprobe's ref counter offset (to test USDT-like logic) which is
not compatible with non-refcounted uprobe. So it's nicer to have each
test uprobe target local to the file and guaranteed to not be inlined or
skipped by the compiler (which can happen with static functions,
especially if compiling selftests with -O2).

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20220126193058.3390292-1-andrii@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 31 insertions, 39 deletions

diff --git a/tools/testing/selftests/bpf/trace_helpers.c b/tools/testing/selftests/bpf/trace_helpers.c
index 7b7f918eda77..65ab533c2516 100644
--- a/tools/testing/selftests/bpf/trace_helpers.c
+++ b/tools/testing/selftests/bpf/trace_helpers.c
@@ -138,6 +138,29 @@ void read_trace_pipe(void)
 	}
 }
 
+ssize_t get_uprobe_offset(const void *addr)
+{
+	size_t start, end, base;
+	char buf[256];
+	bool found;
+	FILE *f;
+
+	f = fopen("/proc/self/maps", "r");
+	if (!f)
+		return -errno;
+
+	while (fscanf(f, "%zx-%zx %s %zx %*[^\n]\n", &start, &end, buf, &base) == 4) {
+		if (buf[2] == 'x' && (uintptr_t)addr >= start && (uintptr_t)addr < end) {
+			found = true;
+			break;
+		}
+	}
+
+	fclose(f);
+
+	if (!found)
+		return -ESRCH;
+
 #if defined(__powerpc64__) && defined(_CALL_ELF) && _CALL_ELF == 2
 
 #define OP_RT_RA_MASK   0xffff0000UL
@@ -145,10 +168,6 @@ void read_trace_pipe(void)
 #define ADDIS_R2_R12    0x3c4c0000UL
 #define ADDI_R2_R2      0x38420000UL
 
-ssize_t get_uprobe_offset(const void *addr, ssize_t base)
-{
-	u32 *insn = (u32 *)(uintptr_t)addr;
-
 	/*
 	 * A PPC64 ABIv2 function may have a local and a global entry
 	 * point. We need to use the local entry point when patching
@@ -165,43 +184,16 @@ ssize_t get_uprobe_offset(const void *addr, ssize_t base)
 	 * lis   r2,XXXX
 	 * addi  r2,r2,XXXX
 	 */
-	if ((((*insn & OP_RT_RA_MASK) == ADDIS_R2_R12) ||
-	     ((*insn & OP_RT_RA_MASK) == LIS_R2)) &&
-	    ((*(insn + 1) & OP_RT_RA_MASK) == ADDI_R2_R2))
-		return (ssize_t)(insn + 2) - base;
-	else
-		return (uintptr_t)addr - base;
-}
-
-#else
+	{
+		const u32 *insn = (const u32 *)(uintptr_t)addr;
 
-ssize_t get_uprobe_offset(const void *addr, ssize_t base)
-{
-	return (uintptr_t)addr - base;
-}
-
-#endif
-
-ssize_t get_base_addr(void)
-{
-	size_t start, offset;
-	char buf[256];
-	FILE *f;
-
-	f = fopen("/proc/self/maps", "r");
-	if (!f)
-		return -errno;
-
-	while (fscanf(f, "%zx-%*x %s %zx %*[^\n]\n",
-		      &start, buf, &offset) == 3) {
-		if (strcmp(buf, "r-xp") == 0) {
-			fclose(f);
-			return start - offset;
-		}
+		if ((((*insn & OP_RT_RA_MASK) == ADDIS_R2_R12) ||
+		     ((*insn & OP_RT_RA_MASK) == LIS_R2)) &&
+		    ((*(insn + 1) & OP_RT_RA_MASK) == ADDI_R2_R2))
+			return (uintptr_t)(insn + 2) - start + base;
 	}
-
-	fclose(f);
-	return -EINVAL;
+#endif
+	return (uintptr_t)addr - start + base;
 }
 
 ssize_t get_rel_offset(uintptr_t addr)