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tunables: Simplify TUNABLE_SET interface

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The TUNABLE_SET interface took a primitive C type argument, which
resulted in inconsistent type conversions internally due to incorrect
dereferencing of types, especialy on 32-bit architectures.  This
change simplifies the TUNABLE setting logic along with the interfaces.

Now all numeric tunable values are stored as signed numbers in
tunable_num_t, which is intmax_t.  All calls to set tunables cast the
input value to its primitive type and then to tunable_num_t for
storage.  This relies on gcc-specific (although I suspect other
compilers woul also do the same) unsigned to signed integer conversion
semantics, i.e. the bit pattern is conserved.  The reverse conversion
is guaranteed by the standard.
This commit is contained in:
Siddhesh Poyarekar
2021-02-05 13:18:58 +05:30
parent e604a5e4bb
commit 61117bfa1b
6 changed files with 76 additions and 128 deletions
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37
elf/dl-tunables.h
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@ -33,9 +33,11 @@ __tunables_init (char **unused __attribute__ ((unused)))
# include <stddef.h>
# include <stdint.h>
typedef intmax_t tunable_num_t;
typedef union
{
int64_t numval;
tunable_num_t numval;
const char *strval;
} tunable_val_t;
@ -52,7 +54,8 @@ typedef void (*tunable_callback_t) (tunable_val_t *);
extern void __tunables_init (char **);
extern void __tunables_print (void);
extern void __tunable_get_val (tunable_id_t, void *, tunable_callback_t);
extern void __tunable_set_val (tunable_id_t, void *, void *, void *);
extern void __tunable_set_val (tunable_id_t, tunable_val_t *, tunable_num_t *,
tunable_num_t *);
rtld_hidden_proto (__tunables_init)
rtld_hidden_proto (__tunables_print)
rtld_hidden_proto (__tunable_get_val)
@ -64,20 +67,18 @@ rtld_hidden_proto (__tunable_set_val)
#if defined TOP_NAMESPACE && defined TUNABLE_NAMESPACE
# define TUNABLE_GET(__id, __type, __cb) \
TUNABLE_GET_FULL (TOP_NAMESPACE, TUNABLE_NAMESPACE, __id, __type, __cb)
# define TUNABLE_SET(__id, __type, __val) \
TUNABLE_SET_FULL (TOP_NAMESPACE, TUNABLE_NAMESPACE, __id, __type, __val)
# define TUNABLE_SET_WITH_BOUNDS(__id, __type, __val, __min, __max) \
# define TUNABLE_SET(__id, __val) \
TUNABLE_SET_FULL (TOP_NAMESPACE, TUNABLE_NAMESPACE, __id, __val)
# define TUNABLE_SET_WITH_BOUNDS(__id, __val, __min, __max) \
TUNABLE_SET_WITH_BOUNDS_FULL (TOP_NAMESPACE, TUNABLE_NAMESPACE, __id, \
__type, __val, __min, __max)
__val, __min, __max)
#else
# define TUNABLE_GET(__top, __ns, __id, __type, __cb) \
TUNABLE_GET_FULL (__top, __ns, __id, __type, __cb)
# define TUNABLE_SET(__top, __ns, __id, __type, __val) \
TUNABLE_SET_FULL (__top, __ns, __id, __type, __val)
# define TUNABLE_SET_WITH_BOUNDS(__top, __ns, __id, __type, __val, \
__min, __max) \
TUNABLE_SET_WITH_BOUNDS_FULL (__top, __ns, __id, __type, __val, \
__min, __max)
# define TUNABLE_SET(__top, __ns, __id, __val) \
TUNABLE_SET_FULL (__top, __ns, __id, __val)
# define TUNABLE_SET_WITH_BOUNDS(__top, __ns, __id, __val, __min, __max) \
TUNABLE_SET_WITH_BOUNDS_FULL (__top, __ns, __id, __val, __min, __max)
#endif
/* Get and return a tunable value. If the tunable was set externally and __CB
@ -91,19 +92,19 @@ rtld_hidden_proto (__tunable_set_val)
})
/* Set a tunable value. */
# define TUNABLE_SET_FULL(__top, __ns, __id, __type, __val) \
# define TUNABLE_SET_FULL(__top, __ns, __id, __val) \
({ \
__tunable_set_val (TUNABLE_ENUM_NAME (__top, __ns, __id), \
& (__type) {__val}, NULL, NULL); \
& (tunable_val_t) {.numval = __val}, NULL, NULL); \
})
/* Set a tunable value together with min/max values. */
# define TUNABLE_SET_WITH_BOUNDS_FULL(__top, __ns, __id, __type, __val, \
__min, __max) \
# define TUNABLE_SET_WITH_BOUNDS_FULL(__top, __ns, __id,__val, __min, __max) \
({ \
__tunable_set_val (TUNABLE_ENUM_NAME (__top, __ns, __id), \
& (__type) {__val}, & (__type) {__min}, \
& (__type) {__max}); \
& (tunable_val_t) {.numval = __val}, \
& (tunable_num_t) {__min}, \
& (tunable_num_t) {__max}); \
})
/* Namespace sanity for callback functions. Use this macro to keep the