x86 (Debugging with GDB)

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#### 21.4.2 x86

`set struct-convention mode`

  Set the convention used by the inferior to return `struct`s and `union`s from functions to mode. Possible values of mode are `"pcc"`, `"reg"`, and `"default"` (the default). `"default"` or `"pcc"` means that `struct`s are returned on the stack, while `"reg"` means that a `struct` or a `union` whose size is 1, 2, 4, or 8 bytes will be returned in a register.

`show struct-convention`

  Show the current setting of the convention to return `struct`s from functions.

#### 21.4.2.1 x87 registers

GDB provides access to the x87 state through the following registers:

- `$st0` to `st7`: `ST(0)` to `ST(7)` floating-point registers
- `$fctrl`: control word register (`FCW`)
- `$fstat`: status word register (`FSW`)
- `$ftag`: tag word (`FTW`)
- `$fiseg`: last instruction pointer segment
- `$fioff`: last instruction pointer
- `$foseg`: last data pointer segment
- `$fooff`: last data pointer
- `$fop`: last opcode