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a=openpgp-sha256; l=4474; i=samitolvanen@google.com; h=from:subject; bh=Ahmj2O3IR+LSl3BiA52xKx3B/l6T0r/Fo4+Nt8cR26I=; b=owEB7QES/pANAwAKAUy19oSLvFbuAcsmYgBmvj04aOj8csDviqueJ1eEjKR7eZPwgInAwuFoD 5HAQqspMuCJAbMEAAEKAB0WIQQ1zPtjsoPW0663g5RMtfaEi7xW7gUCZr49OAAKCRBMtfaEi7xW 7lcUC/9O1P8fFLBUCeOT4Cxm+rBpUW5+73RlFMMG8H+bGc4TSk35d91Su3NehrxYKKU/pT/PVPk DjVOLzLc8vrfvwl1Nt2wQ3EvSJwZZ2eqYER+zrUZkPmdpOjiOYowuBi+VOGnihjQZx8uQsuLUt7 zhIE6Y174Min92jA8j8LDjo3zgA5McorGyWANE2Ma2NOssLU4RB3vC9Cv2K0cJXR5QuckfadlW/ H8vQ6BvRvS05m2JGRSjmSdBZFGPGjJQ6ED/BTajeja7EOvAH4yaTiejmibxBkkf24sQYGkJtIFd 9JRGxIuuBDftKiPVQh0Oy5oK7Bp85TJ10jeczHneuITdV9P5glF6Y93MaLFT/zfIHRIna8eMMht pCs8UVnoc1wLnWExqcs3Q+pdqBXsMgfk0hGBoCKsZS1ot/5/0WRepl1NmMVX+hWHaY52dKgGU/K pA+68yDFF6TmIwfEZNO90AOtKj3WGCZWGirLJ7+tlFKpTSC07C7XYKELv14DkFgF8HGFQ= X-Mailer: git-send-email 2.46.0.184.g6999bdac58-goog Message-ID: <20240815173903.4172139-25-samitolvanen@google.com> Subject: [PATCH v2 04/19] gendwarfksyms: Add support for type pointers From: Sami Tolvanen To: Masahiro Yamada , Luis Chamberlain , Miguel Ojeda , Greg Kroah-Hartman Cc: Matthew Maurer , Alex Gaynor , Wedson Almeida Filho , Gary Guo , Petr Pavlu , Neal Gompa , Hector Martin , Janne Grunau , Asahi Linux , linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org, linux-modules@vger.kernel.org, rust-for-linux@vger.kernel.org, Sami Tolvanen Content-Type: text/plain; charset="UTF-8" The compiler may choose not to emit type information in DWARF for external symbols. Clang, for example, does this for symbols not defined in the current TU. To provide a way to work around this issue, add support for __gendwarfksyms_ptr_ pointers that force the compiler to emit the necessary type information in DWARF also for the missing symbols. Example usage: #define GENDWARFKSYMS_PTR(sym) \ static typeof(sym) *__gendwarfksyms_ptr_##sym __used \ __section(".discard.gendwarfksyms") = &sym; extern int external_symbol(void); GENDWARFKSYMS_PTR(external_symbol); Signed-off-by: Sami Tolvanen --- scripts/gendwarfksyms/dwarf.c | 26 +++++++++++++++++++++++++- scripts/gendwarfksyms/gendwarfksyms.h | 6 ++++++ scripts/gendwarfksyms/symbols.c | 16 ++++++++++++++++ 3 files changed, 47 insertions(+), 1 deletion(-) diff --git a/scripts/gendwarfksyms/dwarf.c b/scripts/gendwarfksyms/dwarf.c index 71cfab0553da..956b30224316 100644 --- a/scripts/gendwarfksyms/dwarf.c +++ b/scripts/gendwarfksyms/dwarf.c @@ -94,6 +94,28 @@ static int process_variable(struct state *state, Dwarf_Die *die) return check(process(state, "variable;\n")); } +static int process_symbol_ptr(struct state *state, Dwarf_Die *die) +{ + Dwarf_Die ptr_type; + Dwarf_Die type; + + if (!get_ref_die_attr(die, DW_AT_type, &ptr_type) || + dwarf_tag(&ptr_type) != DW_TAG_pointer_type) { + error("%s must be a pointer type!", get_name(die)); + return -1; + } + + if (!get_ref_die_attr(&ptr_type, DW_AT_type, &type)) { + error("%s pointer missing a type attribute?", get_name(die)); + return -1; + } + + if (dwarf_tag(&type) == DW_TAG_subroutine_type) + return check(process_subprogram(state, &type)); + else + return check(process_variable(state, &ptr_type)); +} + static int process_exported_symbols(struct state *state, Dwarf_Die *die) { int tag = dwarf_tag(die); @@ -114,7 +136,9 @@ static int process_exported_symbols(struct state *state, Dwarf_Die *die) debug("%s", state->sym->name); - if (tag == DW_TAG_subprogram) + if (is_symbol_ptr(get_name(&state->die))) + check(process_symbol_ptr(state, &state->die)); + else if (tag == DW_TAG_subprogram) check(process_subprogram(state, &state->die)); else check(process_variable(state, &state->die)); diff --git a/scripts/gendwarfksyms/gendwarfksyms.h b/scripts/gendwarfksyms/gendwarfksyms.h index cb9106dfddb9..8f6acd1b8f8f 100644 --- a/scripts/gendwarfksyms/gendwarfksyms.h +++ b/scripts/gendwarfksyms/gendwarfksyms.h @@ -61,6 +61,11 @@ extern bool debug; /* * symbols.c */ + +/* See symbols.c:is_symbol_ptr */ +#define SYMBOL_PTR_PREFIX "__gendwarfksyms_ptr_" +#define SYMBOL_PTR_PREFIX_LEN (sizeof(SYMBOL_PTR_PREFIX) - 1) + struct symbol_addr { uint32_t section; Elf64_Addr address; @@ -78,6 +83,7 @@ struct symbol { struct hlist_node name_hash; }; +extern bool is_symbol_ptr(const char *name); extern int symbol_read_exports(FILE *file); extern int symbol_read_symtab(int fd); extern struct symbol *symbol_get(const char *name); diff --git a/scripts/gendwarfksyms/symbols.c b/scripts/gendwarfksyms/symbols.c index f96acb941196..d6d016458ae1 100644 --- a/scripts/gendwarfksyms/symbols.c +++ b/scripts/gendwarfksyms/symbols.c @@ -41,6 +41,20 @@ static int __for_each_addr(struct symbol *sym, symbol_callback_t func, return processed; } +/* + * For symbols without debugging information (e.g. symbols defined in other + * TUs), we also match __gendwarfksyms_ptr_ symbols, which the + * kernel uses to ensure type information is present in the TU that exports + * the symbol. A __gendwarfksyms_ptr pointer must have the same type as the + * exported symbol, e.g.: + * + * typeof(symname) *__gendwarf_ptr_symname = &symname; + */ +bool is_symbol_ptr(const char *name) +{ + return name && !strncmp(name, SYMBOL_PTR_PREFIX, SYMBOL_PTR_PREFIX_LEN); +} + static int for_each(const char *name, bool name_only, symbol_callback_t func, void *data) { @@ -49,6 +63,8 @@ static int for_each(const char *name, bool name_only, symbol_callback_t func, if (!name || !*name) return 0; + if (is_symbol_ptr(name)) + name += SYMBOL_PTR_PREFIX_LEN; hash_for_each_possible_safe(symbol_names, match, tmp, name_hash, name_hash(name)) { -- 2.46.0.184.g6999bdac58-goog