Re: [Qemu-devel] [PATCH 1/5] configure: move TARGET_*_ALIGNMENT to target-*/cpu.h

[Paolo Bonzini <pbonzini@redhat.com>]

Il 02/04/2013 19:47, Peter Maydell ha scritto:
> On 2 April 2013 18:26, Paolo Bonzini <pbonzini@redhat.com> wrote:
>> I think "a thing the size of a pointer" should be abi_long/ulong.  The
>> pointer is not a CPU concept.
> 
> Yeah. OTOH type alignment isn't a CPU concept either, so I'm
> a little suspicious of these defines in general.

Ok, the main case where the target alignment matters is in 'struct
target_elf_prstatus' (linux-user/elfload.c).

Linux, in its n32 implementation, explicitly uses a different struct
that changes some longs to ints (pr_sigpend, pr_sighold, pr_flag) and
keeps longs for others (pr_reg).

---
typedef unsigned long elf_greg_t;
typedef elf_greg_t elf_gregset_t[ELF_NGREG];

#define elf_prstatus elf_prstatus32
struct elf_prstatus32
{
        struct elf_siginfo pr_info;
        short   pr_cursig;              /* Current signal */
        unsigned int pr_sigpend;        /* Set of pending signals */
        unsigned int pr_sighold;        /* Set of held signals */
        pid_t   pr_pid;
        pid_t   pr_ppid;
        pid_t   pr_pgrp;
        pid_t   pr_sid;
        struct compat_timeval pr_utime; /* User time */
        struct compat_timeval pr_stime; /* System time */
        struct compat_timeval pr_cutime;/* Cumulative user time */
        struct compat_timeval pr_cstime;/* Cumulative system time */
        elf_gregset_t pr_reg;   /* GP registers */
        int pr_fpvalid;
};
---

Instead, we use target_ulong for both (possibly via the
target_elf_greg_t typedef).

sparc32plus and ppc64abi32 instead use 32-bit for pr_reg too (see
include/linux/elfcore-compat.h and fs/compat_binfmt_elf.c).  This is
also wrong.

In any case, what we are doing is doubly wrong.  Things that have 4-byte
alignment should also have 4-byte size.  Things that have 8-byte
alignment should also have 8-byte size.

Paolo