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Diffstat (limited to 'gdb/doc')
| -rw-r--r-- | gdb/doc/ChangeLog | 6 | ||||
| -rw-r--r-- | gdb/doc/gdbint.texinfo | 45 |
2 files changed, 51 insertions, 0 deletions
diff --git a/gdb/doc/ChangeLog b/gdb/doc/ChangeLog index 27d37bd..afd66e6 100644 --- a/gdb/doc/ChangeLog +++ b/gdb/doc/ChangeLog @@ -1,3 +1,9 @@ +2013-06-27 Pedro Alves <palves@redhat.com> + + * gdbint.texinfo (Algorithms) <Stepping over runtime loader + dynamic symbol resolution code>: New section, based on infrun.c + comment. + 2013-06-26 Tom Tromey <tromey@redhat.com> * gdbint.texinfo (Versions and Branches): Use common/version.in. diff --git a/gdb/doc/gdbint.texinfo b/gdb/doc/gdbint.texinfo index 8f82611..749e121 100644 --- a/gdb/doc/gdbint.texinfo +++ b/gdb/doc/gdbint.texinfo @@ -592,6 +592,51 @@ but @code{placed_size} may be. @section Single Stepping +@section Stepping over runtime loader dynamic symbol resolution code +@cindex Procedure Linkage Table, stepping over +@cindex PLT, stepping over +@cindex resolver, stepping over + +If the program uses ELF-style shared libraries, then calls to +functions in shared libraries go through stubs, which live in a table +called the PLT (@dfn{Procedure Linkage Table}). The first time the +function is called, the stub sends control to the dynamic linker, +which looks up the function's real address, patches the stub so that +future calls will go directly to the function, and then passes control +to the function. + +If we are stepping at the source level, we don't want to see any of +this --- we just want to skip over the stub and the dynamic linker. +The simple approach is to single-step until control leaves the dynamic +linker. + +However, on some systems (e.g., Red Hat's 5.2 distribution) the +dynamic linker calls functions in the shared C library, so you can't +tell from the PC alone whether the dynamic linker is still running. +In this case, we use a step-resume breakpoint to get us past the +dynamic linker, as if we were using @code{next} to step over a +function call. + +The @code{in_solib_dynsym_resolve_code} function says whether we're in +the dynamic linker code or not. Normally, this means we single-step. +However, if @code{gdbarch_skip_solib_resolver} then returns non-zero, +then its value is an address where we can place a step-resume +breakpoint to get past the linker's symbol resolution function. + +The @code{in_dynsym_resolve_code} hook of the @code{target_so_ops} +vector can generally be implemented in a pretty portable way, by +comparing the PC against the address ranges of the dynamic linker's +sections. + +The @code{gdbarch_skip_solib_resolver} implementation is generally +going to be system-specific, since it depends on internal details of +the dynamic linker. It's usually not too hard to figure out where to +put a breakpoint, but it certainly isn't portable. +@code{gdbarch_skip_solib_resolver} should do plenty of sanity +checking. If it can't figure things out, returning zero and getting +the (possibly confusing) stepping behavior is better than signaling an +error, which will obscure the change in the inferior's state. */ + @section Signal Handling @section Thread Handling |