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llext: add support for exporting symbols from extensions

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Extensions should be able to selectively export their global symbols.
Add a LL_EXTENSION_SYMBOL() macro for that. Change the present
.sym_tab to be a temporary symbol table of all global symbols in an
extensions, used only during linking for internal purposes. Add a new
.exp_tab symbol table to store symbols, exported by an extension
permanently.

Signed-off-by: Guennadi Liakhovetski <guennadi.liakhovetski@linux.intel.com>
This commit is contained in:
Guennadi Liakhovetski 2023-11-09 14:28:47 +01:00 • committed by Anas Nashif
commit b9bdae8c07
7 changed files with 80 additions and 8 deletions
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12
include/zephyr/llext/llext.h
View file

@ -33,6 +33,7 @@ enum llext_mem {
LLEXT_MEM_DATA,
LLEXT_MEM_RODATA,
LLEXT_MEM_BSS,
LLEXT_MEM_EXPORT,
LLEXT_MEM_SYMTAB,
LLEXT_MEM_STRTAB,
LLEXT_MEM_SHSTRTAB,
@ -60,9 +61,18 @@ struct llext {
/** Total size of the llext memory usage */
size_t mem_size;
/** Exported symbols from the llext, may be linked against by other llext */
/*
* These are all global symbols in the extension, all of them don't
* have to be exported to other extensions, but this table is needed for
* faster internal linking, e.g. if the extension is built out of
* several files, if any symbols are referenced between files, this
* table will be used to link them.
*/
struct llext_symtable sym_tab;
/** Exported symbols from the llext, may be linked against by other llext */
struct llext_symtable exp_tab;
/** Extension use counter, prevents unloading while in use */
unsigned int use_count;
};

2
include/zephyr/llext/loader.h
View file

@ -35,6 +35,8 @@ enum llext_section {
LLEXT_SECT_REL_RODATA,
LLEXT_SECT_REL_BSS,
LLEXT_SECT_EXPORT,
LLEXT_SECT_SYMTAB,
LLEXT_SECT_STRTAB,
LLEXT_SECT_SHSTRTAB,

3
include/zephyr/llext/symbol.h
View file

@ -78,6 +78,9 @@ struct llext_symtable {
.name = STRINGIFY(x), .addr = &x, \
}
#define LL_EXTENSION_SYMBOL(x) struct llext_symbol __attribute__((section(".exported_sym"), used)) \
symbol_##x = {STRINGIFY(x), &x}
/**
* @brief Export a system call to a table of symbols
*

61
subsys/llext/llext.c
View file

@ -75,7 +75,7 @@ struct llext *llext_by_name(const char *name)
const void * const llext_find_sym(const struct llext_symtable *sym_table, const char *sym_name)
{
if (sym_table == NULL) {
/* Buildin symbol table */
/* Built-in symbol table */
STRUCT_SECTION_FOREACH(llext_const_symbol, sym) {
if (strcmp(sym->name, sym_name) == 0) {
return sym->addr;
@ -214,6 +214,9 @@ static int llext_map_sections(struct llext_loader *ldr, struct llext *ext)
} else if (strcmp(name, ".bss") == 0) {
sect_idx = LLEXT_SECT_BSS;
mem_idx = LLEXT_MEM_BSS;
} else if (strcmp(name, ".exported_sym") == 0) {
sect_idx = LLEXT_SECT_EXPORT;
mem_idx = LLEXT_MEM_EXPORT;
} else {
LOG_DBG("Not copied section %s", name);
continue;
@ -240,6 +243,9 @@ static enum llext_section llext_sect_from_mem(enum llext_mem m)
case LLEXT_MEM_RODATA:
s = LLEXT_SECT_RODATA;
break;
case LLEXT_MEM_EXPORT:
s = LLEXT_SECT_EXPORT;
break;
case LLEXT_MEM_TEXT:
s = LLEXT_SECT_TEXT;
break;
@ -401,6 +407,37 @@ static int llext_allocate_symtab(struct llext_loader *ldr, struct llext *ext)
return 0;
}
static int llext_export_symbols(struct llext_loader *ldr, struct llext *ext)
{
elf_shdr_t *shdr = ldr->sects + LLEXT_SECT_EXPORT;
struct llext_symbol *sym;
unsigned int i;
if (shdr->sh_size < sizeof(struct llext_symbol)) {
/* Not found, no symbols exported */
return 0;
}
struct llext_symtable *exp_tab = &ext->exp_tab;
exp_tab->sym_cnt = shdr->sh_size / sizeof(struct llext_symbol);
exp_tab->syms = k_heap_alloc(&llext_heap, exp_tab->sym_cnt * sizeof(struct llext_symbol),
K_NO_WAIT);
if (!exp_tab->syms) {
return -ENOMEM;
}
for (i = 0, sym = ext->mem[LLEXT_MEM_EXPORT];
i < exp_tab->sym_cnt;
i++, sym++) {
exp_tab->syms[i].name = sym->name;
exp_tab->syms[i].addr = sym->addr;
LOG_DBG("sym %p name %s in %p", sym->addr, sym->name, exp_tab->syms + i);
}
return 0;
}
static int llext_copy_symbols(struct llext_loader *ldr, struct llext *ext)
{
size_t ent_size = ldr->sects[LLEXT_SECT_SYMTAB].sh_entsize;
@ -624,6 +661,8 @@ static int llext_link(struct llext_loader *ldr, struct llext *ext, bool do_local
} else if (strcmp(name, ".rel.data") == 0 ||
strcmp(name, ".rela.data") == 0) {
loc = (uintptr_t)ext->mem[LLEXT_MEM_DATA];
} else if (strcmp(name, ".rel.exported_sym") == 0) {
loc = (uintptr_t)ext->mem[LLEXT_MEM_EXPORT];
} else if (strcmp(name, ".rela.plt") == 0 ||
strcmp(name, ".rela.dyn") == 0) {
llext_link_plt(ldr, ext, &shdr, do_local);
@ -679,7 +718,8 @@ static int llext_link(struct llext_loader *ldr, struct llext *ext, bool do_local
name, rel.r_offset, shdr.sh_link);
return -ENODATA;
}
} else if (ELF_ST_TYPE(sym.st_info) == STT_SECTION) {
} else if (ELF_ST_TYPE(sym.st_info) == STT_SECTION ||
ELF_ST_TYPE(sym.st_info) == STT_FUNC) {
/* Current relocation location holds an offset into the section */
link_addr = (uintptr_t)ext->mem[ldr->sect_map[sym.st_shndx]]
+ sym.st_value
@ -719,6 +759,7 @@ static int do_llext_load(struct llext_loader *ldr, struct llext *ext,
memset(ldr->sects, 0, sizeof(ldr->sects));
ldr->sect_cnt = 0;
ext->sym_tab.sym_cnt = 0;
size_t sect_map_sz = ldr->hdr.e_shnum * sizeof(uint32_t);
@ -788,6 +829,12 @@ static int do_llext_load(struct llext_loader *ldr, struct llext *ext,
goto out;
}
ret = llext_export_symbols(ldr, ext);
if (ret != 0) {
LOG_ERR("Failed to export, ret %d", ret);
goto out;
}
out:
k_heap_free(&llext_heap, ldr->sect_map);
@ -798,12 +845,16 @@ out:
k_heap_free(&llext_heap, ext->mem[mem_idx]);
}
}
k_heap_free(&llext_heap, ext->sym_tab.syms);
k_heap_free(&llext_heap, ext->exp_tab.syms);
} else {
LOG_DBG("loaded module, .text at %p, .rodata at %p", ext->mem[LLEXT_MEM_TEXT],
ext->mem[LLEXT_MEM_RODATA]);
}
ext->sym_tab.sym_cnt = 0;
k_heap_free(&llext_heap, ext->sym_tab.syms);
ext->sym_tab.syms = NULL;
return ret;
}
@ -912,7 +963,7 @@ int llext_unload(struct llext **ext)
}
}
k_heap_free(&llext_heap, tmp->sym_tab.syms);
k_heap_free(&llext_heap, tmp->exp_tab.syms);
k_heap_free(&llext_heap, tmp);
return 0;
@ -922,7 +973,7 @@ int llext_call_fn(struct llext *ext, const char *sym_name)
{
void (*fn)(void);
fn = llext_find_sym(&ext->sym_tab, sym_name);
fn = llext_find_sym(&ext->exp_tab, sym_name);
if (fn == NULL) {
return -EINVAL;
}

4
tests/subsys/llext/hello_world/CMakeLists.txt
View file

@ -11,6 +11,8 @@ if(CONFIG_ARM)
add_custom_command(OUTPUT ${PROJECT_BINARY_DIR}/hello_world.llext
COMMAND ${CMAKE_C_COMPILER} ${CMAKE_C_FLAGS} -c
-I ${PROJECT_SOURCE_DIR}/../../../../include
-imacros${PROJECT_BINARY_DIR}/../zephyr/include/generated/autoconf.h
-o ${PROJECT_BINARY_DIR}/hello_world.llext
${PROJECT_SOURCE_DIR}/hello_world.c
)
@ -19,6 +21,8 @@ elseif(CONFIG_XTENSA)
add_custom_command(OUTPUT ${PROJECT_BINARY_DIR}/hello_world.llext
COMMAND ${CMAKE_C_COMPILER} ${CMAKE_C_FLAGS}
-I ${PROJECT_SOURCE_DIR}/../../../../include
-imacros${PROJECT_BINARY_DIR}/../zephyr/include/generated/autoconf.h
-o ${PROJECT_BINARY_DIR}/hello_world.pre.llext
${PROJECT_SOURCE_DIR}/hello_world.c
COMMAND ${CROSS_COMPILE}strip -R .xt.*

4
tests/subsys/llext/hello_world/hello_world.c
View file

@ -12,13 +12,15 @@
*/
#include <stdint.h>
#include <zephyr/llext/symbol.h>
extern void printk(char *fmt, ...);
static const uint32_t number = 42;
extern void hello_world(void)
void hello_world(void)
{
printk("hello world\n");
printk("A number is %lu\n", number);
}
LL_EXTENSION_SYMBOL(hello_world);

2
tests/subsys/llext/src/test_llext_simple.c
View file

@ -38,7 +38,7 @@ ZTEST(llext, test_llext_simple)
zassert_ok(res, "load should succeed");
const void * const hello_world_fn = llext_find_sym(&ext->sym_tab, "hello_world");
const void * const hello_world_fn = llext_find_sym(&ext->exp_tab, "hello_world");
zassert_not_null(hello_world_fn, "hello_world should be an exported symbol");