that emit a nop into the instruction stream, and some data into an auxiliary note section. The data in the note section describes the operands, in terms of size and location. Each location is encoded as assembler operand string. Consumer tools such as gdb or systemtap insert breakpoints on top of the nop, and decode the location operand-strings, like an assembler, to find the values being passed.
The operand strings are selected by the compiler for each operand. They are constrained by gcc inline-assembler codes. The default is:
#define STAP_SDT_ARG_CONSTRAINT nor
This is a good default if the operands tend to be integral and moderate in number (smaller than number of registers). In other cases, the compiler may report "'asm' requires impossible reload" or similar. In this case, consider simplifying the macro call (fewer and simpler operands), reduce optimization, or override the default constraints string via:
#define STAP_SDT_ARG_CONSTRAINT g #include <sys/sdt.h>
#ifdef __ASSEMBLER__ # define _SDT_PROBE(provider, name, n, arglist) \
_SDT_ASM_BODY(provider, name, _SDT_ASM_SUBSTR_1, (_SDT_DEPAREN_##n arglist)) \
_SDT_ASM_BASE # define _SDT_ASM_1(x) x; # define _SDT_ASM_2(a, b) a,b; # define _SDT_ASM_3(a, b, c) a,b,c; # define _SDT_ASM_5(a, b, c, d, e) a,b,c,d,e; # define _SDT_ASM_STRING_1(x) .asciz #x; # define _SDT_ASM_SUBSTR_1(x) .ascii #x; # define _SDT_DEPAREN_0() /* empty */ # define _SDT_DEPAREN_1(a) a # define _SDT_DEPAREN_2(a,b) a b # define _SDT_DEPAREN_3(a,b,c) a b c # define _SDT_DEPAREN_4(a,b,c,d) a b c d # define _SDT_DEPAREN_5(a,b,c,d,e) a b c d e # define _SDT_DEPAREN_6(a,b,c,d,e,f) a b c d e f # define _SDT_DEPAREN_7(a,b,c,d,e,f,g) a b c d e f g # define _SDT_DEPAREN_8(a,b,c,d,e,f,g,h) a b c d e f g h # define _SDT_DEPAREN_9(a,b,c,d,e,f,g,h,i) a b c d e f g h i # define _SDT_DEPAREN_10(a,b,c,d,e,f,g,h,i,j) a b c d e f g h i j # define _SDT_DEPAREN_11(a,b,c,d,e,f,g,h,i,j,k) a b c d e f g h i j k # define _SDT_DEPAREN_12(a,b,c,d,e,f,g,h,i,j,k,l) a b c d e f g h i j k l #else #ifdefined _SDT_HAS_SEMAPHORES #define _SDT_NOTE_SEMAPHORE_USE(provider, name) \
__asm__ __volatile__ ("" :: "m" (provider##_##name##_semaphore)); #else #define _SDT_NOTE_SEMAPHORE_USE(provider, name) #endif
/* NB: gdb PR24541 highlighted an unspecified corner of the sdt.h operand note format.
The named register may be a longer or shorter (!) alias for the storage where the value in question is found. For example, on i386, 64-bit value may be put in register pairs, and the register name stored would identify just one of them. Previously, gcc was asked to emit the %w[id] (16-bit alias of some registers holding operands), even when a wider 32-bit value was used.
Bottom line: the byte-width given before the @ sign governs. If there is a mismatch between that width and that of the named register, then a sys/sdt.h note consumer may need to employ architecture-specific heuristics to figure out where the compiler has actually put the complete value.
*/
/* If the assembler supports the necessary feature, then we can play nice with code in COMDAT sections, which comes up in C++ code. Without that assembler support, some combinations of probe placements
in certain kinds of C++ code may produce link-time errors. */ #include"sdt-config.h" #if _SDT_ASM_SECTION_AUTOGROUP_SUPPORT # define _SDT_ASM_AUTOGROUP "?" #else # define _SDT_ASM_AUTOGROUP "" #endif
/* This STAP_PROBEV macro can be used in variadic scenarios, where the number of probe arguments is not known until compile time. Since variadic macro support may vary with compiler options, you must pre-#define SDT_USE_VARIADIC to enable this type of probe.
Note that our _SDT_NARG is called with an extra 0 arg that's not counted, so we don't have to worry about the behavior of macros
called without any arguments. */
#define _SDT_NARG(...) __SDT_NARG(__VA_ARGS__, 12,11,10,9,8,7,6,5,4,3,2,1,0) #define __SDT_NARG(_0,_1,_2,_3,_4,_5,_6,_7,_8,_9,_10,_11,_12, N, ...) N #ifdef SDT_USE_VARIADIC #define _SDT_PROBE_N(provider, name, N, ...) \
_SDT_PROBE(provider, name, N, (__VA_ARGS__)) #define STAP_PROBEV(provider, name, ...) \
_SDT_PROBE_N(provider, name, _SDT_NARG(0, ##__VA_ARGS__), ##__VA_ARGS__) #endif
/* These macros are for use in asm statements. You must compile with -std=gnu99 or -std=c99 to use the STAP_PROBE_ASM macro.
The STAP_PROBE_ASM macro generates a quoted string to be used in the template portion of the asm statement, concatenated with strings that contain the actual assembly code around the probe site.
emits the assembly code for "before\nafter", with a probe in between. The probe arguments are the %eax register, and the value of the memory word located 4 bytes past the address in the %esi register. Note that because this is a simple asm, not a GNU C extended asm statement, these % characters do not need to be doubled to generate literal %reg names.
In a GNU C extended asm statement, the probe arguments can be specified using the macro STAP_PROBE_ASM_TEMPLATE(n) for n arguments. The paired macro STAP_PROBE_ASM_OPERANDS gives the C values of these probe arguments, and appears in the input operand list of the asm statement. For example:
but the probe site is right between "someinsn" and "otherinsn".
The probe arguments in STAP_PROBE_ASM can be given as assembly operands instead, even inside a GNU C extended asm statement. Note that these can use operand templates like %0 or %[name],
and likewise they must write %%reg for a literal operand of %reg. */
Die Informationen auf dieser Webseite wurden
nach bestem Wissen sorgfältig zusammengestellt. Es wird jedoch weder Vollständigkeit, noch Richtigkeit,
noch Qualität der bereit gestellten Informationen zugesichert.
Bemerkung:
Die farbliche Syntaxdarstellung und die Messung sind noch experimentell.