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22.7 Configuring the Current ABI

GDB can determine the ABI (Application Binary Interface) of your application automatically. However, sometimes you need to override its conclusions. Use these commands to manage GDB’s view of the current ABI.

One GDB configuration can debug binaries for multiple operating system targets, either via remote debugging or native emulation. GDB will autodetect the OS ABI (Operating System ABI) in use, but you can override its conclusion using the set osabi command. One example where this is useful is in debugging of binaries which use an alternate C library (e.g. UCLIBC for GNU/Linux) which does not have the same identifying marks that the standard C library for your platform provides.

When GDB is debugging the AArch64 architecture, it provides a “Newlib” OS ABI. This is useful for handling setjmp and longjmp when debugging binaries that use the NEWLIB C library. The “Newlib” OS ABI can be selected by set osabi Newlib.

show osabi

Show the OS ABI currently in use.

set osabi

With no argument, show the list of registered available OS ABI’s.

set osabi abi

Set the current OS ABI to abi.

Generally, the way that an argument of type float is passed to a function depends on whether the function is prototyped. For a prototyped (i.e. ANSI/ISO style) function, float arguments are passed unchanged, according to the architecture’s convention for float. For unprototyped (i.e. K&R style) functions, float arguments are first promoted to type double and then passed.

Unfortunately, some forms of debug information do not reliably indicate whether a function is prototyped. If GDB calls a function that is not marked as prototyped, it consults set coerce-float-to-double.

set coerce-float-to-double
set coerce-float-to-double on

Arguments of type float will be promoted to double when passed to an unprototyped function. This is the default setting.

set coerce-float-to-double off

Arguments of type float will be passed directly to unprototyped functions.

show coerce-float-to-double

Show the current setting of promoting float to double.

GDB needs to know the ABI used for your program’s C++ objects. The correct C++ ABI depends on which C++ compiler was used to build your application. GDB only fully supports programs with a single C++ ABI; if your program contains code using multiple C++ ABI’s or if GDB can not identify your program’s ABI correctly, you can tell GDB which ABI to use. Currently supported ABI’s include “gnu-v2”, for g++ versions before 3.0, “gnu-v3”, for g++ versions 3.0 and later, and “hpaCC” for the HP ANSI C++ compiler. Other C++ compilers may use the “gnu-v2” or “gnu-v3” ABI’s as well. The default setting is “auto”.

show cp-abi

Show the C++ ABI currently in use.

set cp-abi

With no argument, show the list of supported C++ ABI’s.

set cp-abi abi
set cp-abi auto

Set the current C++ ABI to abi, or return to automatic detection.

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