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The program’s block structure is represented by the N_LBRAC (left
brace) and the N_RBRAC (right brace) stab types. The variables
defined inside a block precede the N_LBRAC symbol for most
compilers, including GCC. Other compilers, such as the Convex, Acorn
RISC machine, and Sun acc compilers, put the variables after the
N_LBRAC symbol. The values of the N_LBRAC and
N_RBRAC symbols are the start and end addresses of the code of
the block, respectively. For most machines, they are relative to the
starting address of this source file. For the Gould NP1, they are
absolute. For stabs in sections (see Using Stabs in Their Own Sections), they are
relative to the function in which they occur.
The N_LBRAC and N_RBRAC stabs that describe the block
scope of a procedure are located after the N_FUN stab that
represents the procedure itself.
Sun documents the desc field of N_LBRAC and
N_RBRAC symbols as containing the nesting level of the block.
However, dbx seems to not care, and GCC always sets desc to
zero.
For XCOFF, block scope is indicated with C_BLOCK symbols. If the
name of the symbol is ‘.bb’, then it is the beginning of the block;
if the name of the symbol is ‘.be’; it is the end of the block.