Em Mon, Jan 30, 2023 at 03:36:09PM -0300, Arnaldo Carvalho de Melo escreveu:
> Em Mon, Jan 30, 2023 at 02:29:41PM +0000, Alan Maguire escreveu:
> > Compilation generates DWARF at several stages, and often the
> > later DWARF representations more accurately represent optimizations
> > that have occurred during compilation.
> >
> > In particular, parameter representations can be spotted by their
> > abstract origin references to the original parameter, but they
> > often have more accurate location information. In most cases,
> > the parameter locations will match calling conventions, and be
> > registers for the first 6 parameters on x86_64, first 8 on ARM64
> > etc. If the parameter is not a register when it should be however,
> > it is likely passed via the stack or the compiler has used a
> > constant representation instead. The latter can often be
> > spotted by checking for a DW_AT_const_value attribute,
> > as noted by Eduard.
> >
> > In addition, absence of a location tag (either across
> > the abstract origin reference and the original parameter,
> > or in the standalone parameter description) is evidence of
> > an optimized-out parameter. Presence of a location tag
> > is stored in the parameter description and shared between
> > abstract tags and their original referents.
> >
> > This change adds a field to parameters and their associated
> > ftype to note if a parameter has been optimized out. Having
> > this information allows us to skip such functions, as their
> > presence in CUs makes BTF encoding impossible.
> >
> > Signed-off-by: Alan Maguire <alan.maguire@xxxxxxxxxx>
> > ---
> > dwarf_loader.c | 125 +++++++++++++++++++++++++++++++++++++++++++++++++++++----
> > dwarves.h | 5 ++-
> > 2 files changed, 122 insertions(+), 8 deletions(-)
> >
> > diff --git a/dwarf_loader.c b/dwarf_loader.c
> > index 5a74035..93c2307 100644
> > --- a/dwarf_loader.c
> > +++ b/dwarf_loader.c
> > @@ -992,13 +992,98 @@ static struct class_member *class_member__new(Dwarf_Die *die, struct cu *cu,
> > return member;
> > }
> >
> > -static struct parameter *parameter__new(Dwarf_Die *die, struct cu *cu, struct conf_load *conf)
> > +/* How many function parameters are passed via registers? Used below in
> > + * determining if an argument has been optimized out or if it is simply
> > + * an argument > NR_REGISTER_PARAMS. Setting NR_REGISTER_PARAMS to 0
> > + * allows unsupported architectures to skip tagging optimized-out
> > + * values.
> > + */
> > +#if defined(__x86_64__)
> > +#define NR_REGISTER_PARAMS 6
> > +#elif defined(__s390__)
> > +#define NR_REGISTER_PARAMS 5
> > +#elif defined(__aarch64__)
> > +#define NR_REGISTER_PARAMS 8
> > +#elif defined(__mips__)
> > +#define NR_REGISTER_PARAMS 8
> > +#elif defined(__powerpc__)
> > +#define NR_REGISTER_PARAMS 8
> > +#elif defined(__sparc__)
> > +#define NR_REGISTER_PARAMS 6
> > +#elif defined(__riscv) && __riscv_xlen == 64
> > +#define NR_REGISTER_PARAMS 8
> > +#elif defined(__arc__)
> > +#define NR_REGISTER_PARAMS 8
> > +#else
> > +#define NR_REGISTER_PARAMS 0
> > +#endif
>
> This should be done as a function, something like:
>
> int cu__nr_register_params(struct cu *cu)
> {
> GElf_Ehdr ehdr;
>
> gelf_getehdr(cu->elf, &ehdr);
>
> switch (ehdr.machine) {
> ...
>
> }
>
> I'm coding that now, will send the diff shortly.
>
> This is to support cross-builds.
I made this change to this patch, please check.
Thanks,
- Arnaldo
diff --git a/dwarf_loader.c b/dwarf_loader.c
index 752a3c1afc4494f2..81963e71715c8435 100644
--- a/dwarf_loader.c
+++ b/dwarf_loader.c
@@ -994,29 +994,29 @@ static struct class_member *class_member__new(Dwarf_Die *die, struct cu *cu,
/* How many function parameters are passed via registers? Used below in
* determining if an argument has been optimized out or if it is simply
- * an argument > NR_REGISTER_PARAMS. Setting NR_REGISTER_PARAMS to 0
- * allows unsupported architectures to skip tagging optimized-out
+ * an argument > cu__nr_register_params(). Making cu__nr_register_params()
+ * return 0 allows unsupported architectures to skip tagging optimized-out
* values.
*/
-#if defined(__x86_64__)
-#define NR_REGISTER_PARAMS 6
-#elif defined(__s390__)
-#define NR_REGISTER_PARAMS 5
-#elif defined(__aarch64__)
-#define NR_REGISTER_PARAMS 8
-#elif defined(__mips__)
-#define NR_REGISTER_PARAMS 8
-#elif defined(__powerpc__)
-#define NR_REGISTER_PARAMS 8
-#elif defined(__sparc__)
-#define NR_REGISTER_PARAMS 6
-#elif defined(__riscv) && __riscv_xlen == 64
-#define NR_REGISTER_PARAMS 8
-#elif defined(__arc__)
-#define NR_REGISTER_PARAMS 8
-#else
-#define NR_REGISTER_PARAMS 0
-#endif
+static int arch__nr_register_params(const GElf_Ehdr *ehdr)
+{
+ switch (ehdr->e_machine) {
+ case EM_S390: return 5;
+ case EM_SPARC:
+ case EM_SPARCV9:
+ case EM_X86_64: return 6;
+ case EM_AARCH64:
+ case EM_ARC:
+ case EM_ARM:
+ case EM_MIPS:
+ case EM_PPC:
+ case EM_PPC64:
+ case EM_RISCV: return 8;
+ default: break;
+ }
+
+ return 0;
+}
static struct parameter *parameter__new(Dwarf_Die *die, struct cu *cu,
struct conf_load *conf, int param_idx)
@@ -1031,7 +1031,7 @@ static struct parameter *parameter__new(Dwarf_Die *die, struct cu *cu,
tag__init(&parm->tag, cu, die);
parm->name = attr_string(die, DW_AT_name, conf);
- if (param_idx >= NR_REGISTER_PARAMS)
+ if (param_idx >= cu->nr_register_params)
return parm;
/* Parameters which use DW_AT_abstract_origin to point at
* the original parameter definition (with no name in the DIE)
@@ -2870,6 +2870,7 @@ static int cu__set_common(struct cu *cu, struct conf_load *conf,
return DWARF_CB_ABORT;
cu->little_endian = ehdr.e_ident[EI_DATA] == ELFDATA2LSB;
+ cu->nr_register_params = arch__nr_register_params(&ehdr);
return 0;
}
diff --git a/dwarves.h b/dwarves.h
index fd1ca3ae9f4ab531..ddf56f0124e0ec03 100644
--- a/dwarves.h
+++ b/dwarves.h
@@ -262,6 +262,7 @@ struct cu {
uint8_t has_addr_info:1;
uint8_t uses_global_strings:1;
uint8_t little_endian:1;
+ uint8_t nr_register_params;
uint16_t language;
unsigned long nr_inline_expansions;
size_t size_inline_expansions;
