[Mesa-dev] [PATCH] amd/rtld: update the ELF representation of LDS symbols

[Nicolai Hähnle]

From: Nicolai Hähnle <nicolai.haehnle at amd.com>

The initial prototype used a processor-specific symbol type, but
feedback suggests that an approach using processor-specific section
name that encodes the alignment analogous to SHN_COMMON symbols is
preferred.

This patch keeps both variants around for now to reduce problems
with LLVM compatibility as we switch branches around.

This also cleans up the error reporting in this function.
---
 src/amd/common/ac_rtld.c | 30 ++++++++++++++++++++++++------
 1 file changed, 24 insertions(+), 6 deletions(-)

diff --git a/src/amd/common/ac_rtld.c b/src/amd/common/ac_rtld.c
index dc9cc04705b..6379e55120d 100644
--- a/src/amd/common/ac_rtld.c
+++ b/src/amd/common/ac_rtld.c
@@ -32,21 +32,25 @@
 
 #include "ac_binary.h"
 #include "ac_gpu_info.h"
 #include "util/u_dynarray.h"
 #include "util/u_math.h"
 
 // Old distributions may not have this enum constant
 #define MY_EM_AMDGPU 224
 
 #ifndef STT_AMDGPU_LDS
-#define STT_AMDGPU_LDS 13
+#define STT_AMDGPU_LDS 13 // this is deprecated -- remove
+#endif
+
+#ifndef SHN_AMDGPU_LDS
+#define SHN_AMDGPU_LDS 0xff00
 #endif
 
 #ifndef R_AMDGPU_NONE
 #define R_AMDGPU_NONE 0
 #define R_AMDGPU_ABS32_LO 1
 #define R_AMDGPU_ABS32_HI 2
 #define R_AMDGPU_ABS64 3
 #define R_AMDGPU_REL32 4
 #define R_AMDGPU_REL64 5
 #define R_AMDGPU_ABS32 6
@@ -169,47 +173,60 @@ static bool layout_symbols(struct ac_rtld_symbol *symbols, unsigned num_symbols,
  * Read LDS symbols from the given \p section of the ELF of \p part and append
  * them to the LDS symbols list.
  *
  * Shared LDS symbols are filtered out.
  */
 static bool read_private_lds_symbols(struct ac_rtld_binary *binary,
 				     unsigned part_idx,
 				     Elf_Scn *section,
 				     uint32_t *lds_end_align)
 {
-#define report_elf_if(cond) \
+#define report_if(cond) \
 	do { \
 		if ((cond)) { \
 			report_errorf(#cond); \
 			return false; \
 		} \
 	} while (false)
+#define report_elf_if(cond) \
+	do { \
+		if ((cond)) { \
+			report_elf_errorf(#cond); \
+			return false; \
+		} \
+	} while (false)
 
 	struct ac_rtld_part *part = &binary->parts[part_idx];
 	Elf64_Shdr *shdr = elf64_getshdr(section);
 	uint32_t strtabidx = shdr->sh_link;
 	Elf_Data *symbols_data = elf_getdata(section, NULL);
 	report_elf_if(!symbols_data);
 
 	const Elf64_Sym *symbol = symbols_data->d_buf;
 	size_t num_symbols = symbols_data->d_size / sizeof(Elf64_Sym);
 
 	for (size_t j = 0; j < num_symbols; ++j, ++symbol) {
-		if (ELF64_ST_TYPE(symbol->st_info) != STT_AMDGPU_LDS)
+		struct ac_rtld_symbol s = {};
+
+		if (ELF64_ST_TYPE(symbol->st_info) == STT_AMDGPU_LDS) {
+			/* old-style LDS symbols from initial prototype -- remove eventually */
+			s.align = MIN2(1u << (symbol->st_other >> 3), 1u << 16);
+		} else if (symbol->st_shndx == SHN_AMDGPU_LDS) {
+			s.align = MIN2(symbol->st_value, 1u << 16);
+			report_if(!util_is_power_of_two_nonzero(s.align));
+		} else
 			continue;
 
-		report_elf_if(symbol->st_size > 1u << 29);
+		report_if(symbol->st_size > 1u << 29);
 
-		struct ac_rtld_symbol s = {};
 		s.name = elf_strptr(part->elf, strtabidx, symbol->st_name);
 		s.size = symbol->st_size;
-		s.align = MIN2(1u << (symbol->st_other >> 3), 1u << 16);
 		s.part_idx = part_idx;
 
 		if (!strcmp(s.name, "__lds_end")) {
 			report_elf_if(s.size != 0);
 			*lds_end_align = MAX2(*lds_end_align, s.align);
 			continue;
 		}
 
 		const struct ac_rtld_symbol *shared =
 			find_symbol(&binary->lds_symbols, s.name, part_idx);
@@ -217,20 +234,21 @@ static bool read_private_lds_symbols(struct ac_rtld_binary *binary,
 			report_elf_if(s.align > shared->align);
 			report_elf_if(s.size > shared->size);
 			continue;
 		}
 
 		util_dynarray_append(&binary->lds_symbols, struct ac_rtld_symbol, s);
 	}
 
 	return true;
 
+#undef report_if
 #undef report_elf_if
 }
 
 /**
  * Open a binary consisting of one or more shader parts.
  *
  * \param binary the uninitialized struct
  * \param i binary opening parameters
  */
 bool ac_rtld_open(struct ac_rtld_binary *binary,
-- 
2.20.1