Hi Mark, On Thu, Sep 4, 2025 at 1:12 PM Mark Wielaard <m...@klomp.org> wrote: > > Hi Aaron, > > On Mon, 2025-08-04 at 23:24 -0400, Aaron Merey wrote: > > Signed-off-by: Aaron Merey <ame...@redhat.com> > > --- > > v2: Remove mention of implementation details. Mention that conversion > > to native byte order and direct access alignment resembles elf_getdata. > > Mention elf_errmsg. > > > > On Mon, Jul 7, 2025 at 1:26 PM Mark Wielaard <m...@klomp.org> wrote: > > > > > > Nice overview of ELF data types. But might there be a better place for > > > this? I would assume elf_data, but that man page is currently very bare > > > bones. > > > > When I update the bare bones man pages including elf_data I'll move > > the Elf_Type description there. > > Thanks. > > > > Speaking of thread safety... > > > This should be MT-Safe and documented that way. > > > > > > But is it really? > > > The code takes a read lock on elf->lock. Checks whether it can find an > > > existing Elf_Data_Chunk. If yes, it returns that one. Which seems fine. > > > But if not it inserts the dummy chunk without actually data, > > > allocates/creates the data, drops the rdlock (!), takes a write lock > > > and overwrites the dummy chunk with the real data, drops the lock again > > > and returns the data. > > > > > > What if at (!) another call gets the read lock first before the current > > > thread can (re)take the write lock? That other thread could find the > > > existing dummy key already in the cache and return the dummy data? > > > > I've posted a patch that fixes this race condition. > > I cannot find it, could you repost it please?
I wrote the patch but didn't actually send it to the list! It's now sent: https://sourceware.org/pipermail/elfutils-devel/2025q3/008527.html > > > doc/Makefile.am | 1 + > > doc/elf_getdata_rawchunk.3 | 140 +++++++++++++++++++++++++++++++++++++ > > 2 files changed, 141 insertions(+) > > create mode 100644 doc/elf_getdata_rawchunk.3 > > > > diff --git a/doc/Makefile.am b/doc/Makefile.am > > index 791a68da..fbe69980 100644 > > --- a/doc/Makefile.am > > +++ b/doc/Makefile.am > > @@ -67,6 +67,7 @@ notrans_dist_man3_MANS= elf32_checksum.3 \ > > elf_getarsym.3 \ > > elf_getbase.3 \ > > elf_getdata.3 \ > > + elf_getdata_rawchunk.3 \ > > elf_getscn.3 \ > > elf_hash.3 \ > > elf_kind.3 \ > > OK. > > > diff --git a/doc/elf_getdata_rawchunk.3 b/doc/elf_getdata_rawchunk.3 > > new file mode 100644 > > index 00000000..9660b1f1 > > --- /dev/null > > +++ b/doc/elf_getdata_rawchunk.3 > > @@ -0,0 +1,140 @@ > > +.TH ELF_GETDATA_RAWCHUNK 3 2025-06-30 "Libelf" "Libelf Programmer's Manual" > > + > > +.SH NAME > > +elf_getdata_rawchunk \- create a raw data descriptor from a file offset > > + > > +.SH SYNOPSIS > > +.nf > > +#include <libelf.h> > > + > > +.B Elf_Data * elf_getdata_rawchunk("Elf *elf", "int64_t offset", "size_t > > size", "Elf_Type type"); > > +.fi > > OK. > > > +.SH DESCRIPTION > > +The > > +.BR elf_getdata_rawchunk () > > +function returns an > > +.B Elf_Data > > +descriptor that refers to a raw region of the ELF file, starting at the > > +given file > > +.I offset > > +and spanning > > +.I size > > +bytes. This is used to access arbitrary byte ranges in the ELF file that > > may > > +not correspond to any section or segment. > > + > > +The returned > > +.B Elf_Data > > +.I d_buf > > +will be properly aligned for the requested > > +.IR type . > > + > > +If the file’s byte order matches the host, and alignment permits, the raw > > data is > > +returned as-is. If the file’s byte order differs, the buffer is converted > > into native > > +byte order and aligned for direct access. This behaves like > > +.BR elf_getdata (), > > +and not > > +.BR elf_rawdata (). > > +The contents of the return value's > > +.I d_buf > > +are a decoded representation. > > + > > +The returned data is not associated with any section or update mechanism. > > It will not > > +be included in any output written by > > +.BR elf_update (3). > > +It is also owned by libelf and is valid until > > +.BR elf_end () > > +is called on > > +.IR elf . > > OK. > > > +.SH PARAMETERS > > +.TP > > +.I elf > > +A pointer to an > > +.B Elf > > +descriptor representing the ELF file. > > + > > +.TP > > +.I offset > > +The starting file offset in bytes. This must lie within the bounds of the > > file. > > + > > +.TP > > +.I size > > +The number of bytes to include in the data chunk, starting at > > +.IR offset . > > + > > +.TP > > +.I type > > +An > > +.B Elf_Type > > +enumeration value indicating the intended interpretation of the data. > > Values include: > > + > > +.RS > > +.TP > > +.B ELF_T_BYTE > > +Raw bytes. > > +.TP > > +.B ELF_T_ADDR, ELF_T_OFF, ELF_T_HALF, ELF_T_WORD, ELF_T_XWORD, > > ELF_T_SWORD, ELF_T_SXWORD > > +Integer and pointer types. > > +.TP > > +.B ELF_T_EHDR, ELF_T_SHDR, ELF_T_PHDR > > +ELF file, section, and program headers. > > +.TP > > +.B ELF_T_SYM, ELF_T_DYN, ELF_T_REL, ELF_T_RELA, ELF_T_RELR > > +Symbols and relocations. > > +.TP > > +.B ELF_T_NHDR, ELF_T_CHDR, ELF_T_NHDR8 > > +ELF note headers and compressed data headers. > > +.TP > > +.B ELF_T_VDEF, ELF_T_VDAUX, ELF_T_VNEED, ELF_T_VNAUX > > +Versioning structures. > > +.TP > > +.B ELF_T_SYMINFO, ELF_T_MOVE, ELF_T_LIB > > +Other ELF metadata. > > +.TP > > +.B ELF_T_GNUHASH > > +GNU-style hash table. > > +.TP > > +.B ELF_T_AUXV > > +Auxiliary vectors. > > +.RE > > OK. > > > +.SH RETURN VALUE > > +Returns a pointer to an > > +.B Elf_Data > > +descriptor on success. > > + > > +Returns NULL if any arguments are invalid, or if memory allocation or file > > reading > > +fails. An error code is set which can be retrieved with > > +.BR elf_errmsg (). > > +The result is cached and shared between repeated calls using the same > > arguments. > > OK. > > > +.SH SEE ALSO > > +.BR elf (3), > > +.BR elf_errmsg (3), > > +.BR elf_getdata (3), > > +.BR elf_getscn (3), > > +.BR elf_rawdata (3), > > +.BR libelf (3), > > +.BR elf (5) > > OK. > > > +.SH ATTRIBUTES > > +.TS > > +allbox; > > +lbx lb lb > > +l l l. > > +Interface Attribute Value > > +T{ > > +.na > > +.nh > > +.BR elf_getdata_rawchunk () > > +T} Thread safety MT-Safe > > +.TE > > + > > +.SH REPORTING BUGS > > +Report bugs to <elfutils-devel@sourceware.org> or > > https://sourceware.org/bugzilla/. > > + > > +.SH HISTORY > > +.B elf_getdata_rawchunk > > +first appeared in elfutils 0.130. This function is a elfutils libelf > > extension and > > +may not be available in other libelf implementations. > > OK. >
