Differences between GNU stabs in a.out and GNU stabs in xcoff

(The AIX/RS6000 native object file format is xcoff with stabs)

• Instead of .stabs, xcoff uses .stabx.
• The data fields of an xcoff .stabx are in a different order than an a.out .stabs. The order is: string, value, type. The desc and null fields present in a.out stabs are missing in xcoff stabs. For N_GSYM the value field is the name of the symbol.
• BSD a.out stab types correspond to AIX xcoff storage classes. In general the mapping is N_STABTYPE becomes C_STABTYPE. Some stab types in a.out are not supported in xcoff. See Table E. for full mappings. exception: initialised static N_STSYM and un-initialized static N_LCSYM both map to the C_STSYM storage class. But the destinction is preserved because in xcoff N_STSYM and N_LCSYM must be emited in a named static block. Begin the block with .bs s[RW] data_section_name for N_STSYM or .bs s bss_section_name for N_LCSYM. End the block with .es
• xcoff stabs describing tags and typedefs use the N_DECL (0x8c)instead of N_LSYM stab type.
• xcoff uses N_RPSYM (0x8e) instead of the N_RSYM stab type for register variables. If the register variable is also a value parameter, then use R instead of P for the symbol descriptor. 6. xcoff uses negative numbers as type references to the basic types. There are no boilerplate type definitions emited for these basic types. << make table of basic types and type numbers for C >>
• xcoff .stabx sometimes don't have the name part of the string field.
• xcoff uses a .file stab type to represent the source file name. There is no stab for the path to the source file.
• xcoff uses a .line stab type to represent source lines. The format is: .line line_number.
• xcoff emits line numbers relative to the start of the current function. The start of a function is marked by .bf. If a function includes lines from a seperate file, then those line numbers are absolute line numbers in the <<sub-?>> file being compiled.
• The start of current include file is marked with: .bi "filename" and the end marked with .ei "filename"
• If the xcoff stab is a N_FUN (C_FUN) then follow the string field with ,. instead of just ,
• The symbol descriptor for register parameters is P for a.out and R for xcoff.

(I think that's it for .s file differences. They could stand to be better presented. This is just a list of what I have noticed so far. There are a *lot* of differences in the information in the symbol tables of the executable and object files.)

Table E: mapping a.out stab types to xcoff storage classes

stab type       storage class
-------------------------------
N_GSYM          C_GSYM
N_FNAME         unknown
N_FUN           C_FUN
N_STSYM         C_STSYM
N_LCSYM         C_STSYM
N_MAIN          unkown
N_PC            unknown
N_RSYM          C_RSYM
N_RPSYM (0x8e)  C_RPSYM 
N_M2C           unknown
N_SLINE         unknown
N_DSLINE        unknown
N_BSLINE        unknown
N_BROWSE        unchanged
N_CATCH         unknown
N_SSYM          unknown
N_SO            unknown
N_LSYM          C_LSYM
N_DECL  (0x8c)  C_DECL 
N_BINCL         unknown
N_SOL           unknown
N_PSYM          C_PSYM
N_EINCL         unknown
N_ENTRY         C_ENTRY
N_LBRAC         unknown
N_EXCL          unknown
N_SCOPE         unknown
N_RBRAC         unknown
N_BCOMM         C_BCOMM
N_ECOMM         C_ECOMM
N_ECOML         C_ECOML

N_LENG          unknown