Fix ELF ABI and endianness checks for powerpc64

Earlier, it was assumed that ELF ABI v2 is used only on
little-endian powerpc64 environments but it seems this
ABI can be used independently of endianness.

It is expected that any C preprocessor that conforms to
the ELF ABI v2 specification must predefine the _CALL_ELF
macro and set its value to 2.

Instead of looking at __BYTE_ORDER__ to determine whether
to use the Local Entry Point (LEP) of symbols, one should
look at the _CALL_ELF macro instead as this is ABI-related.

Similarly, _CALL_ELF should be used only for determining
the ABI version and not the endianness.

Reported-by: Naveen N. Rao <[email protected]>
Fixes: bbd4180 ("Fix uprobes on powerpc64")
Fixes: 1086952 ("clang: Add support to build eBPF for user specified ARCH")
Acked-by: Naveen N. Rao <[email protected]>
Signed-off-by: Sandipan Das <[email protected]>

Author: sandip4n

src/cc/bcc_elf.c

@@ -257,16 +257,8 @@ static int list_in_scn(Elf *e, Elf_Scn *section, size_t stridx, size_t symsize,
         continue;
 
 #ifdef __powerpc64__
-#if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
-      if (opddata && sym.st_shndx == opdidx) {
-        size_t offset = sym.st_value - opdshdr.sh_addr;
-        /* Find the function descriptor */
-        uint64_t *descr = opddata->d_buf + offset;
-        /* Read the actual entry point address from the descriptor */
-        sym.st_value = *descr;
-      }
-#elif __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
-      if (option->use_symbol_type & (1 << STT_PPC64LE_SYM_LEP)) {
+#if defined(_CALL_ELF) && _CALL_ELF == 2
+      if (option->use_symbol_type & (1 << STT_PPC64_ELFV2_SYM_LEP)) {
         /*
          * The PowerPC 64-bit ELF v2 ABI says that the 3 most significant bits
          * in the st_other field of the symbol table specifies the number of
@@ -287,6 +279,14 @@ static int list_in_scn(Elf *e, Elf_Scn *section, size_t stridx, size_t symsize,
           case 6: sym.st_value += 64; break;
         }
       }
+#else
+      if (opddata && sym.st_shndx == opdidx) {
+        size_t offset = sym.st_value - opdshdr.sh_addr;
+        /* Find the function descriptor */
+        uint64_t *descr = opddata->d_buf + offset;
+        /* Read the actual entry point address from the descriptor */
+        sym.st_value = *descr;
+      }
 #endif
 #endif
 

src/cc/bcc_syms.cc

@@ -712,8 +712,8 @@ int bcc_resolve_symname(const char *module, const char *symname,
     .use_debug_file = 1,
     .check_debug_file_crc = 1,
     .lazy_symbolize = 1,
-#if defined(__powerpc64__) && __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
-    .use_symbol_type = BCC_SYM_ALL_TYPES | (1 << STT_PPC64LE_SYM_LEP),
+#if defined(__powerpc64__) && defined(_CALL_ELF) && _CALL_ELF == 2
+    .use_symbol_type = BCC_SYM_ALL_TYPES | (1 << STT_PPC64_ELFV2_SYM_LEP),
 #else
     .use_symbol_type = BCC_SYM_ALL_TYPES,
 #endif

src/cc/bcc_syms.h

@@ -38,10 +38,10 @@ struct mod_info;
 #define STT_GNU_IFUNC 10
 #endif
 
-#if defined(__powerpc64__) && __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
+#if defined(__powerpc64__) && defined(_CALL_ELF) && _CALL_ELF == 2
 // Indicate if the Local Entry Point (LEP) should be used as a symbol's
 // start address
-#define STT_PPC64LE_SYM_LEP 31
+#define STT_PPC64_ELFV2_SYM_LEP 31
 #endif
 
 static const uint32_t BCC_SYM_ALL_TYPES = 65535;

src/cc/frontends/clang/arch_helper.h

@@ -34,7 +34,7 @@ static void *run_arch_callback(arch_callback_t fn)
   /* If ARCH is not set, detect from local arch clang is running on */
   if (!archenv) {
 #if defined(__powerpc64__)
-#if defined(_CALL_ELF) && _CALL_ELF == 2
+#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
     return fn(BCC_ARCH_PPC_LE);
 #else
     return fn(BCC_ARCH_PPC);
@@ -50,7 +50,7 @@ static void *run_arch_callback(arch_callback_t fn)
 
   /* Otherwise read it from ARCH */
   if (!strcmp(archenv, "powerpc")) {
-#if defined(_CALL_ELF) && _CALL_ELF == 2
+#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
     return fn(BCC_ARCH_PPC_LE);
 #else
     return fn(BCC_ARCH_PPC);

tests/cc/test_c_api.cc

@@ -205,8 +205,8 @@ TEST_CASE("resolve symbol addresses for a given PID", "[c_api]") {
     .use_debug_file = 1,
     .check_debug_file_crc = 1,
     .lazy_symbolize = 1,
-#if defined(__powerpc64__) && __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
-    .use_symbol_type = BCC_SYM_ALL_TYPES | (1 << STT_PPC64LE_SYM_LEP),
+#if defined(__powerpc64__) && defined(_CALL_ELF) && _CALL_ELF == 2
+    .use_symbol_type = BCC_SYM_ALL_TYPES | (1 << STT_PPC64_ELFV2_SYM_LEP),
 #else
     .use_symbol_type = BCC_SYM_ALL_TYPES,
 #endif