[Cbe-oss-dev] [PATCH] libspe2: Extended __ea support

[Alan Modra]

This patch teaches libspe2 how to perform a (very) limited set of
SPU relocations in order to support stand-alone execution of SPU
programs that make use of new __ea variables.  For those who haven't
used the SPU gcc __ea support, __ea variables and pointers are a way for
the SPU to access PPU memory transparently via a software managed cache.
Current SPU gcc only allows extern __ea variables.  You need to define
the variable in a PPU program and embed the SPU executable to make it
all work.  I'm in the process of extending this to allow the SPU program
to define the __ea variables.  They'll be placed in a special
non-allocated section, so the section doesn't occupy space in the SPU
local store, but does do so in the file image.  When embedded, this
section naturally occupies space in PPU memory and so gives the __ea
variables their memory allocation.  When standalone, the SPU executable
is mmap'd by libspe, so the section also occupies PPU memory.  All
libspe needs to do is let the SPU know the PPU memory locations, which
is accomplished by applying these relocations.

Signed-off-by: Alan Modra <amodra at bigpond.net.au>

-- 
Alan Modra
Australia Development Lab, IBM

diff -urp libspe2-2.2.80.orig/spebase/elf_loader.c libspe2-2.2.80/spebase/elf_loader.c
--- libspe2-2.2.80.orig/spebase/elf_loader.c	2008-03-25 22:30:47.000000000 +1030
+++ libspe2-2.2.80/spebase/elf_loader.c	2008-04-11 15:54:44.000000000 +0930
@@ -197,6 +197,44 @@ copy_to_ld_buffer(spe_program_handle_t *
 	DEBUG_PRINTF("done ...\n");
 }
 
+/* Apply certain R_SPU_PPU* relocs in RH to SH.  We only handle relocs
+   without a symbol, which are to locations within ._ea.  */
+
+static void
+apply_relocations(spe_program_handle_t *handle, Elf32_Shdr *rh, Elf32_Shdr *sh)
+{
+#define R_SPU_PPU32 15
+#define R_SPU_PPU64 16
+	void *start = handle->elf_image;
+	Elf32_Rela *r, *r_end;
+	/* Relocations in an executable specify r_offset as a virtual
+	   address, but we are applying the reloc in the image before
+	   the section has been copied to its destination sh_addr.
+	   Adjust so as to poke relative to the image base.  */
+	void *reloc_base = start + sh->sh_offset - sh->sh_addr;
+
+	r = start + rh->sh_offset;
+	r_end = (void *)r + rh->sh_size;
+	DEBUG_PRINTF("apply_relocations: %p, %#x\n", r, rh->sh_size);
+	for (; r < r_end; ++r)
+	{
+		if (r->r_info == ELF32_R_INFO(0,R_SPU_PPU32)) {
+			Elf32_Word *loc = reloc_base + r->r_offset;
+			Elf32_Word v = (Elf32_Word)(long)start + r->r_addend;
+			/* Don't dirty pages unnecessarily.  */
+			if (*loc != v)
+				*loc = v;
+			DEBUG_PRINTF("PPU32(%p) = %#x\n", loc, v);
+		} else if (r->r_info == ELF32_R_INFO(0,R_SPU_PPU32)) {
+			Elf64_Xword *loc = reloc_base + r->r_offset;
+			Elf64_Xword v = (Elf64_Xword)(long)start + r->r_addend;
+			if (*loc != v)
+				*loc = v;
+			DEBUG_PRINTF("PPU64(%p) = %#llx\n", loc, v);
+		}
+	}
+}
+
 int
 _base_spe_load_spe_elf (spe_program_handle_t *handle, void *ld_buffer, struct spe_ld_info *ld_info)
 {
@@ -237,6 +275,8 @@ _base_spe_load_spe_elf (spe_program_hand
 	for (sh = shdr; sh < &shdr[ehdr->e_shnum]; ++sh)
 	{
 		DEBUG_PRINTF("section name: %s ( start: 0x%04x, size: 0x%04x)\n", str_table+sh->sh_name, sh->sh_offset, sh->sh_size );
+		if (sh->sh_type == SHT_RELA)
+			apply_relocations(handle, sh, &shdr[sh->sh_info]);
 		if (strcmp(".toe", str_table+sh->sh_name) == 0) {
 			DEBUG_PRINTF("section offset: %d\n", sh->sh_offset);
 			toe_size += sh->sh_size;