diff options
Diffstat (limited to 'include')
| -rw-r--r-- | include/libc-symbols.h | 142 |
1 files changed, 126 insertions, 16 deletions
diff --git a/include/libc-symbols.h b/include/libc-symbols.h index e362d42095..6ae309a1ba 100644 --- a/include/libc-symbols.h +++ b/include/libc-symbols.h @@ -737,27 +737,137 @@ for linking") # define compat_data_section .section ".data.compat", "aw"; #endif -/* Marker used for indirection function symbols. */ -#define libc_ifunc(name, expr) \ - extern void *name##_ifunc (void) __asm__ (#name); \ - void *name##_ifunc (void) \ +/* Helper / base macros for indirect function symbols. */ +#define __ifunc_resolver(type_name, name, expr, arg, init, classifier) \ + classifier void *name##_ifunc (arg) \ { \ - INIT_ARCH (); \ - __typeof (name) *res = expr; \ + init (); \ + __typeof (type_name) *res = expr; \ return res; \ - } \ - __asm__ (".type " #name ", %gnu_indirect_function"); + } + +#ifdef HAVE_GCC_IFUNC +# define __ifunc(type_name, name, expr, arg, init) \ + extern __typeof (type_name) name __attribute__ \ + ((ifunc (#name "_ifunc"))); \ + __ifunc_resolver (type_name, name, expr, arg, init, static) + +# define __ifunc_hidden(type_name, name, expr, arg, init) \ + __ifunc (type_name, name, expr, arg, init) +#else +/* Gcc does not support __attribute__ ((ifunc (...))). Use the old behaviour + as fallback. But keep in mind that the debug information for the ifunc + resolver functions is not correct. It contains the ifunc'ed function as + DW_AT_linkage_name. E.g. lldb uses this field and an inferior function + call of the ifunc'ed function will fail due to "no matching function for + call to ..." because the ifunc'ed function and the resolver function have + different signatures. (Gcc support is disabled at least on a ppc64le + Ubuntu 14.04 system.) */ + +# define __ifunc(type_name, name, expr, arg, init) \ + extern __typeof (type_name) name; \ + void *name##_ifunc (arg) __asm__ (#name); \ + __ifunc_resolver (type_name, name, expr, arg, init,) \ + __asm__ (".type " #name ", %gnu_indirect_function"); + +# define __ifunc_hidden(type_name, name, expr, arg, init) \ + extern __typeof (type_name) __libc_##name; \ + __ifunc (type_name, __libc_##name, expr, arg, init) \ + strong_alias (__libc_##name, name); +#endif /* !HAVE_GCC_IFUNC */ + +/* The following macros are used for indirect function symbols in libc.so. + First of all, you need to have the function prototyped somewhere, + say in foo.h: + + int foo (int __bar); + + If you have an implementation for foo which e.g. uses a special hardware + feature which isn't available on all machines where this libc.so will be + used but decideable if available at runtime e.g. via hwcaps, you can provide + two or multiple implementations of foo: + + int __foo_default (int __bar) + { + return __bar; + } + + int __foo_special (int __bar) + { + return __bar; + } + + If your function foo has no libc_hidden_proto (foo) defined for PLT + bypassing, you can use: + + #define INIT_ARCH() unsigned long int hwcap = __GLRO(dl_hwcap); + + libc_ifunc (foo, (hwcap & HWCAP_SPECIAL) ? __foo_special : __foo_default); + + This will define a resolver function for foo which returns __foo_special or + __foo_default depending on your specified expression. Please note that you + have to define a macro function INIT_ARCH before using libc_ifunc macro as + it is called by the resolver function before evaluating the specified + expression. In this example it is used to prepare the hwcap variable. + The resolver function is assigned to an ifunc'ed symbol foo. Calls to foo + from inside or outside of libc.so will be indirected by a PLT call. + + If your function foo has a libc_hidden_proto (foo) defined for PLT bypassing + and calls to foo within libc.so should always go to one specific + implementation of foo e.g. __foo_default then you have to add: + + __hidden_ver1 (__foo_default, __GI_foo, __foo_default); + + or a tweaked definition of libc_hidden_def macro after the __foo_default + function definition. Calls to foo within libc.so will always go directly to + __foo_default. Calls to foo from outside libc.so will be indirected by a + PLT call to ifunc'ed symbol foo which you have to define in a separate + compile unit: + + #define foo __redirect_foo + #include <foo.h> + #undef foo + + extern __typeof (__redirect_foo) __foo_default attribute_hidden; + extern __typeof (__redirect_foo) __foo_special attribute_hidden; + + libc_ifunc_redirected (__redirect_foo, foo, + (hwcap & HWCAP_SPECIAL) + ? __foo_special + : __foo_default); + + This will define the ifunc'ed symbol foo like above. The redirection of foo + in header file is needed to omit an additional defintion of __GI_foo which + would end in a linker error while linking libc.so. You have to specify + __redirect_foo as first parameter which is used within libc_ifunc_redirected + macro in conjunction with typeof to define the ifunc'ed symbol foo. + + If your function foo has a libc_hidden_proto (foo) defined and calls to foo + within or from outside libc.so should go via ifunc'ed symbol, then you have + to use: + + libc_ifunc_hidden (foo, foo, + (hwcap & HWCAP_SPECIAL) + ? __foo_special + : __foo_default); + libc_hidden_def (foo) + + The first parameter foo of libc_ifunc_hidden macro is used in the same way + as for libc_ifunc_redirected macro. */ + +#define libc_ifunc(name, expr) __ifunc (name, name, expr, void, INIT_ARCH) + +#define libc_ifunc_redirected(redirected_name, name, expr) \ + __ifunc (redirected_name, name, expr, void, INIT_ARCH) + +#define libc_ifunc_hidden(redirected_name, name, expr) \ + __ifunc_hidden (redirected_name, name, expr, void, INIT_ARCH) /* The body of the function is supposed to use __get_cpu_features which will, if necessary, initialize the data first. */ -#define libm_ifunc(name, expr) \ - extern void *name##_ifunc (void) __asm__ (#name); \ - void *name##_ifunc (void) \ - { \ - __typeof (name) *res = expr; \ - return res; \ - } \ - __asm__ (".type " #name ", %gnu_indirect_function"); +#define libm_ifunc_init() +#define libm_ifunc(name, expr) \ + __ifunc (name, name, expr, void, libm_ifunc_init) #ifdef HAVE_ASM_SET_DIRECTIVE # define libc_ifunc_hidden_def1(local, name) \ |