Fix kldxref failing for modules with a short mc_cval

[mhorne063_gmail.com]

Summary

Attempting to retrieve an md_cval string from a kernel module with
kldxref would throw a offset error for modules created using lld, since
this value would be placed at the end of all allocated sections.

Add an ef_read_seg_string method to the ef interface, to allow reading
strings of varying size without attempting to read beyond the segment's
bounds.

Bugzilla

[mhorne063_gmail.com]

Upload diff correctly with tabs and full context

[cem]

usr.sbin/kldxref/ef.c

516 ↗

(On Diff #37990)

why would ofs be -1? Other methods don't seem to check for this condition.

517 ↗

(On Diff #37990)

Why lseek+read instead of ef_read or pread?

527 ↗

(On Diff #37990)

inconsistent return style -- probably just remove parens

usr.sbin/kldxref/ef_obj.c

312 ↗

(On Diff #37990)

same as above (s.a.)

316 ↗

(On Diff #37990)

is this a tab?

[emaste]

usr.sbin/kldxref/ef.c

516 ↗

(On Diff #37990)

ef_read uses (Elf_Off)-1 to mean "no seek", this keeps the same interface

527 ↗

(On Diff #37990)

kldxref is already quite inconsistent; I count 47 return ( and 66 return [^(]. IMO it makes sense to follow style(9) when there's this much existing inconsistency.

[cem]

usr.sbin/kldxref/ef.c

527 ↗

(On Diff #37990)

That's an ok theory I can get behind, but this patch isn't internally consistent either. See the two returns directly above (0).

[emaste]

usr.sbin/kldxref/ef.c

527 ↗

(On Diff #37990)

Fair enough, the patch should at least be self-consistent.

[mhorne063_gmail.com]

usr.sbin/kldxref/ef.c

517 ↗

(On Diff #37990)

ef_read expects to read a certain length and returns an error if it comes up short, which is what we are working around here. On the other hand, pread seems slightly cleaner for this purpose so I will update it to use that.

[emaste]

usr.sbin/kldxref/ef.c

517 ↗

(On Diff #37990)

Note that in the earlier patch we accepted (Elf_Off)-1 as "no seek", and that precluded using pread. But we don't need this for strings so Mitchell dropped it.

[kib]

usr.sbin/kldxref/ef.c

104 ↗

(On Diff #38036)

I t is tempting to use the chance and switch to designated initializers.

506 ↗

(On Diff #38036)

No initialization in declarations.

Wny u_long ?

518 ↗

(On Diff #38036)

Why not return errno there ?

532 ↗

(On Diff #38036)

Again, why not return (errno) ?

[mhorne063_gmail.com]

A lot of these comments address issues/inconsistencies already present in the source. I will create a subsequent cleanup patch to address these but follow what is there at the moment for this patch, since @emaste wants this merged to fix the lld build process.

[cem]

usr.sbin/kldxref/ef.c

506 ↗

(On Diff #38036)

Matches existing style of file -- ok for now, IMO.