[ARM/FDPIC v3 06/21] [ARM] FDPIC: Add support for c++ exceptions
Richard Earnshaw (lists)
Richard.Earnshaw@arm.com
Fri Oct 12 11:54:00 GMT 2018
On 11/10/18 14:34, Christophe Lyon wrote:
> The main difference with existing support is that function addresses
> are function descriptor addresses instead. This means that all code
> dealing with function pointers now has to cope with function
> descriptors instead.
>
> For the same reason, Linux kernel helpers can no longer be called by
> dereferencing their address, so we implement the same functionality as
> a regular function here.
>
> When restoring a function address, we also have to restore the FDPIC
> register value (r9).
>
> 2018-XX-XX Christophe Lyon <christophe.lyon@st.com>
> Mickaël Guêné <mickael.guene@st.com>
>
> gcc/
> * ginclude/unwind-arm-common.h (unwinder_cache): Add reserved5
> field.
> (FDPIC_REGNUM): New define.
>
> libgcc/
> * config/arm/linux-atomic.c (__kernel_cmpxchg): Add FDPIC support.
> (__kernel_dmb): Likewise.
> (__fdpic_cmpxchg): New function.
> (__fdpic_dmb): New function.
> * config/arm/unwind-arm.h (gnu_Unwind_Find_got): New function.
> (_Unwind_decode_typeinfo_ptr): Add FDPIC support.
> * unwindo-arm-common.inc (UCB_PR_GOT): New.
> (funcdesc_t): New struct.
> (get_eit_entry): Add FDPIC support.
> (unwind_phase2): Likewise.
> (unwind_phase2_forced): Likewise.
> (__gnu_Unwind_RaiseException): Likewise.
> (__gnu_Unwind_Resume): Likewise.
> (__gnu_Unwind_Backtrace): Likewise.
> * unwind-pe.h (read_encoded_value_with_base): Likewise.
>
> libstdc++/
> * libsupc++/eh_personality.cc (get_ttype_entry): Add FDPIC
> support.
>
> Change-Id: I517a49ff18fae21c686cd1c6008ea7974515b347
>
> diff --git a/gcc/ginclude/unwind-arm-common.h b/gcc/ginclude/unwind-arm-common.h
> index 8a1a919..f663891 100644
> --- a/gcc/ginclude/unwind-arm-common.h
> +++ b/gcc/ginclude/unwind-arm-common.h
> @@ -91,7 +91,7 @@ extern "C" {
> _uw reserved2; /* Personality routine address */
> _uw reserved3; /* Saved callsite address */
> _uw reserved4; /* Forced unwind stop arg */
> - _uw reserved5;
> + _uw reserved5; /* Personality routine GOT value in FDPIC mode. */
> }
> unwinder_cache;
> /* Propagation barrier cache (valid after phase 1): */
> @@ -247,4 +247,6 @@ typedef unsigned long _uleb128_t;
> } /* extern "C" */
> #endif
>
> +#define FDPIC_REGNUM 9
Looking at the rest of this file, I think it can end up being included
in user code. So you have to put predefines into the reserved
namespace. Why do you need this here anyway?
> +
> #endif /* defined UNWIND_ARM_COMMON_H */
> diff --git a/libgcc/config/arm/linux-atomic.c b/libgcc/config/arm/linux-atomic.c
> index d334c58..161d1ce 100644
> --- a/libgcc/config/arm/linux-atomic.c
> +++ b/libgcc/config/arm/linux-atomic.c
> @@ -25,11 +25,49 @@ see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
>
> /* Kernel helper for compare-and-exchange. */
> typedef int (__kernel_cmpxchg_t) (int oldval, int newval, int *ptr);
> +#if __FDPIC__
> +/* Non-FDPIC ABIs call __kernel_cmpxchg directly by dereferencing its
> + address, but under FDPIC we would generate a broken call
> + sequence. That's why we have to implement __kernel_cmpxchg and
> + __kernel_dmb here: this way, the FDPIC call sequence works. */
> +#define __kernel_cmpxchg __fdpic_cmpxchg
> +#else
> #define __kernel_cmpxchg (*(__kernel_cmpxchg_t *) 0xffff0fc0)
> +#endif
>
> /* Kernel helper for memory barrier. */
> typedef void (__kernel_dmb_t) (void);
> +#if __FDPIC__
> +#define __kernel_dmb __fdpic_dmb
> +#else
> #define __kernel_dmb (*(__kernel_dmb_t *) 0xffff0fa0)
> +#endif
> +
> +#if __FDPIC__
> +static int __fdpic_cmpxchg (int oldval, int newval, int *ptr)
> +{
> + int result;
> +
> + asm volatile ("1: ldrex r3, [%[ptr]]\n\t"
> + "subs r3, r3, %[oldval]\n\t"
> + "itt eq\n\t"
> + "strexeq r3, %[newval], [%[ptr]]\n\t"
> + "teqeq r3, #1\n\t"
> + "it eq\n\t"
> + "beq 1b\n\t"
> + "rsbs %[result], r3, #0\n\t"
> + : [result] "=r" (result)
> + : [oldval] "r" (oldval) , [newval] "r" (newval), [ptr] "r" (ptr)
> + : "r3");
> + return result;
> +}
> +
> +static void __fdpic_dmb ()
> +{
> + asm volatile ("dmb\n\t");
> +}
> +
The whole point of __kernel_dmb and __kernel_cmpxchg is that the kernel
can map in a code sequence specific to the runtime CPU. This ensures
that the right sequence is used for that CPU. This breaks that
principle entirely.
> +#endif
>
> /* Note: we implement byte, short and int versions of atomic operations using
> the above kernel helpers; see linux-atomic-64bit.c for "long long" (64-bit)
> diff --git a/libgcc/config/arm/unwind-arm.h b/libgcc/config/arm/unwind-arm.h
> index 9f7d3f2..db5dfa2 100644
> --- a/libgcc/config/arm/unwind-arm.h
> +++ b/libgcc/config/arm/unwind-arm.h
> @@ -33,9 +33,31 @@
> /* Use IP as a scratch register within the personality routine. */
> #define UNWIND_POINTER_REG 12
>
> +#define STR(x) #x
> +#define XSTR(x) STR(x)
> +
> #ifdef __cplusplus
> extern "C" {
> #endif
> +_Unwind_Ptr __attribute__((weak)) __gnu_Unwind_Find_got (_Unwind_Ptr);
> +
> +static inline _Unwind_Ptr gnu_Unwind_Find_got (_Unwind_Ptr ptr)
> +{
> + _Unwind_Ptr res;
> +
> + if (__gnu_Unwind_Find_got)
> + res = __gnu_Unwind_Find_got (ptr);
> + else
> + {
> + asm volatile ("mov %[result], r" XSTR(FDPIC_REGNUM)
> + : [result]"=r" (res)
> + :
> + :);
> + }
> +
> + return res;
> +}
> +
> /* Decode an R_ARM_TARGET2 relocation. */
> static inline _Unwind_Word
> _Unwind_decode_typeinfo_ptr (_Unwind_Word base __attribute__ ((unused)),
> @@ -48,7 +70,12 @@ extern "C" {
> if (!tmp)
> return 0;
>
> -#if (defined(linux) && !defined(__uClinux__)) || defined(__NetBSD__) \
> +#if __FDPIC__
> + /* For FDPIC, we store the offset of the GOT entry. */
> + /* So, first get GOT from dynamic linker and then use indirect access. */
> + tmp += gnu_Unwind_Find_got (ptr);
> + tmp = *(_Unwind_Word *) tmp;
> +#elif (defined(linux) && !defined(__uClinux__)) || defined(__NetBSD__) \
> || defined(__FreeBSD__) || defined(__fuchsia__)
> /* Pc-relative indirect. */
> #define _GLIBCXX_OVERRIDE_TTYPE_ENCODING (DW_EH_PE_pcrel | DW_EH_PE_indirect)
> diff --git a/libgcc/unwind-arm-common.inc b/libgcc/unwind-arm-common.inc
> index 76f8fc3..7187edd 100644
> --- a/libgcc/unwind-arm-common.inc
> +++ b/libgcc/unwind-arm-common.inc
> @@ -62,6 +62,7 @@ __gnu_Unwind_Find_exidx (_Unwind_Ptr, int *);
> #define UCB_PR_ADDR(ucbp) ((ucbp)->unwinder_cache.reserved2)
> #define UCB_SAVED_CALLSITE_ADDR(ucbp) ((ucbp)->unwinder_cache.reserved3)
> #define UCB_FORCED_STOP_ARG(ucbp) ((ucbp)->unwinder_cache.reserved4)
> +#define UCB_PR_GOT(ucbp) ((ucbp)->unwinder_cache.reserved5)
>
> /* Unwind descriptors. */
>
> @@ -85,6 +86,15 @@ typedef struct __EIT_entry
> _uw content;
> } __EIT_entry;
>
> +#ifdef __FDPIC__
> +
> +/* Only used in FDPIC case. */
> +struct funcdesc_t {
> + unsigned int ptr;
> + unsigned int got;
> +};
This isn't in GNU style.
> +#endif
> +
> /* Assembly helper functions. */
>
> /* Restore core register state. Never returns. */
> @@ -259,7 +269,21 @@ get_eit_entry (_Unwind_Control_Block *ucbp, _uw return_address)
> {
> /* One of the predefined standard routines. */
> _uw idx = (*(_uw *) ucbp->pr_cache.ehtp >> 24) & 0xf;
> +#if __FDPIC__
> + {
> + struct funcdesc_t *funcdesc
> + = (struct funcdesc_t *) __gnu_unwind_get_pr_addr (idx);
> + if (funcdesc)
> + {
> + UCB_PR_ADDR (ucbp) = funcdesc->ptr;
> + UCB_PR_GOT (ucbp) = funcdesc->got;
> + }
> + else
> + UCB_PR_ADDR (ucbp) = 0;
> + }
> +#else
> UCB_PR_ADDR (ucbp) = __gnu_unwind_get_pr_addr (idx);
> +#endif
> if (UCB_PR_ADDR (ucbp) == 0)
> {
> /* Failed */
> @@ -270,6 +294,10 @@ get_eit_entry (_Unwind_Control_Block *ucbp, _uw return_address)
> {
> /* Execute region offset to PR */
> UCB_PR_ADDR (ucbp) = selfrel_offset31 (ucbp->pr_cache.ehtp);
> +#if __FDPIC__
> + UCB_PR_GOT (ucbp)
> + = (unsigned int) gnu_Unwind_Find_got ((_Unwind_Ptr) UCB_PR_ADDR (ucbp));
> +#endif
> }
> return _URC_OK;
> }
> @@ -291,14 +319,29 @@ unwind_phase2 (_Unwind_Control_Block * ucbp, phase2_vrs * vrs)
> UCB_SAVED_CALLSITE_ADDR (ucbp) = VRS_PC(vrs);
>
> /* Call the pr to decide what to do. */
> +#if __FDPIC__
> + {
> + volatile struct funcdesc_t funcdesc;
> + funcdesc.ptr = UCB_PR_ADDR (ucbp);
> + funcdesc.got = UCB_PR_GOT (ucbp);
> + pr_result = ((personality_routine) &funcdesc)
> + (_US_UNWIND_FRAME_STARTING, ucbp, (_Unwind_Context *) vrs);
> + }
> +#else
> pr_result = ((personality_routine) UCB_PR_ADDR (ucbp))
> (_US_UNWIND_FRAME_STARTING, ucbp, (_Unwind_Context *) vrs);
> +#endif
> }
> while (pr_result == _URC_CONTINUE_UNWIND);
>
> if (pr_result != _URC_INSTALL_CONTEXT)
> abort();
>
> +#if __FDPIC__
> + /* r9 could have been lost due to PLT jump. Restore correct value. */
> + vrs->core.r[FDPIC_REGNUM] = gnu_Unwind_Find_got (VRS_PC (vrs));
> +#endif
> +
> uw_restore_core_regs (vrs, &vrs->core);
> }
>
> @@ -346,8 +389,18 @@ unwind_phase2_forced (_Unwind_Control_Block *ucbp, phase2_vrs *entry_vrs,
> next_vrs = saved_vrs;
>
> /* Call the pr to decide what to do. */
> +#if __FDPIC__
> + {
> + volatile struct funcdesc_t funcdesc;
> + funcdesc.ptr = UCB_PR_ADDR (ucbp);
> + funcdesc.got = UCB_PR_GOT (ucbp);
> + pr_result = ((personality_routine) &funcdesc)
> + (action, ucbp, (void *) &next_vrs);
> + }
> +#else
> pr_result = ((personality_routine) UCB_PR_ADDR (ucbp))
> (action, ucbp, (void *) &next_vrs);
> +#endif
>
> saved_vrs.prev_sp = VRS_SP (&next_vrs);
> }
> @@ -384,6 +437,11 @@ unwind_phase2_forced (_Unwind_Control_Block *ucbp, phase2_vrs *entry_vrs,
> return _URC_FAILURE;
> }
>
> +#if __FDPIC__
> + /* r9 could have been lost due to PLT jump. Restore correct value. */
> + saved_vrs.core.r[FDPIC_REGNUM] = gnu_Unwind_Find_got (VRS_PC (&saved_vrs));
> +#endif
> +
> uw_restore_core_regs (&saved_vrs, &saved_vrs.core);
> }
>
> @@ -429,8 +487,18 @@ __gnu_Unwind_RaiseException (_Unwind_Control_Block * ucbp,
> return _URC_FAILURE;
>
> /* Call the pr to decide what to do. */
> +#if __FDPIC__
> + {
> + volatile struct funcdesc_t funcdesc;
> + funcdesc.ptr = UCB_PR_ADDR (ucbp);
> + funcdesc.got = UCB_PR_GOT (ucbp);
> + pr_result = ((personality_routine) &funcdesc)
> + (_US_VIRTUAL_UNWIND_FRAME, ucbp, (void *) &saved_vrs);
> + }
> +#else
> pr_result = ((personality_routine) UCB_PR_ADDR (ucbp))
> (_US_VIRTUAL_UNWIND_FRAME, ucbp, (void *) &saved_vrs);
> +#endif
> }
> while (pr_result == _URC_CONTINUE_UNWIND);
>
> @@ -488,13 +556,27 @@ __gnu_Unwind_Resume (_Unwind_Control_Block * ucbp, phase2_vrs * entry_vrs)
> }
>
> /* Call the cached PR. */
> +#if __FDPIC__
> + {
> + volatile struct funcdesc_t funcdesc;
> + funcdesc.ptr = UCB_PR_ADDR (ucbp);
> + funcdesc.got = UCB_PR_GOT (ucbp);
> + pr_result = ((personality_routine) &funcdesc)
> + (_US_UNWIND_FRAME_RESUME, ucbp, (_Unwind_Context *) entry_vrs);
> + }
> +#else
> pr_result = ((personality_routine) UCB_PR_ADDR (ucbp))
> (_US_UNWIND_FRAME_RESUME, ucbp, (_Unwind_Context *) entry_vrs);
> +#endif
>
> switch (pr_result)
> {
> case _URC_INSTALL_CONTEXT:
> /* Upload the registers to enter the landing pad. */
> +#if __FDPIC__
> + /* r9 could have been lost due to PLT jump. Restore correct value. */
> + entry_vrs->core.r[FDPIC_REGNUM] = gnu_Unwind_Find_got (VRS_PC (entry_vrs));
> +#endif
> uw_restore_core_regs (entry_vrs, &entry_vrs->core);
>
> case _URC_CONTINUE_UNWIND:
> @@ -586,9 +668,20 @@ __gnu_Unwind_Backtrace(_Unwind_Trace_Fn trace, void * trace_argument,
> }
>
> /* Call the pr to decide what to do. */
> +#if __FDPIC__
> + {
> + volatile struct funcdesc_t funcdesc;
> + funcdesc.ptr = UCB_PR_ADDR (ucbp);
> + funcdesc.got = UCB_PR_GOT (ucbp);
> + code = ((personality_routine) &funcdesc)
> + (_US_VIRTUAL_UNWIND_FRAME | _US_FORCE_UNWIND,
> + ucbp, (void *) &saved_vrs);
> + }
> +#else
> code = ((personality_routine) UCB_PR_ADDR (ucbp))
> (_US_VIRTUAL_UNWIND_FRAME | _US_FORCE_UNWIND,
> ucbp, (void *) &saved_vrs);
> +#endif
> }
> while (code != _URC_END_OF_STACK
> && code != _URC_FAILURE);
> diff --git a/libgcc/unwind-pe.h b/libgcc/unwind-pe.h
> index dd5ae95..9c5177f 100644
> --- a/libgcc/unwind-pe.h
> +++ b/libgcc/unwind-pe.h
> @@ -259,10 +259,27 @@ read_encoded_value_with_base (unsigned char encoding, _Unwind_Ptr base,
>
> if (result != 0)
> {
> +#if __FDPIC__
> + /* FDPIC relative addresses imply taking the GOT address
> + into account. */
> + if ((encoding & DW_EH_PE_pcrel) && (encoding & DW_EH_PE_indirect))
> + {
> + result += gnu_Unwind_Find_got ((_Unwind_Ptr) u);
> + result = *(_Unwind_Internal_Ptr *) result;
> + }
> + else
> + {
> + result += ((encoding & 0x70) == DW_EH_PE_pcrel
> + ? (_Unwind_Internal_Ptr) u : base);
> + if (encoding & DW_EH_PE_indirect)
> + result = *(_Unwind_Internal_Ptr *) result;
> + }
> +#else
> result += ((encoding & 0x70) == DW_EH_PE_pcrel
> ? (_Unwind_Internal_Ptr) u : base);
> if (encoding & DW_EH_PE_indirect)
> result = *(_Unwind_Internal_Ptr *) result;
> +#endif
> }
> }
>
> diff --git a/libstdc++-v3/libsupc++/eh_personality.cc b/libstdc++-v3/libsupc++/eh_personality.cc
> index 1b336c7..7b26b8d 100644
> --- a/libstdc++-v3/libsupc++/eh_personality.cc
> +++ b/libstdc++-v3/libsupc++/eh_personality.cc
> @@ -93,7 +93,15 @@ get_ttype_entry (lsda_header_info *info, _uleb128_t i)
> _Unwind_Ptr ptr;
>
> i *= size_of_encoded_value (info->ttype_encoding);
> - read_encoded_value_with_base (info->ttype_encoding, info->ttype_base,
> + read_encoded_value_with_base (
> +#if __FDPIC__
> + /* Force these flags to nake sure to
> + take the GOT into account. */
> + (DW_EH_PE_pcrel | DW_EH_PE_indirect),
> +#else
> + info->ttype_encoding,
> +#endif
> + info->ttype_base,
> info->TType - i, &ptr);
>
> return reinterpret_cast<const std::type_info *>(ptr);
>
Nearly all of the above is outside of my comfort zone... I can't help
feeling that there ought to be a less invasive way to do this, but
without being particularly familiar with the code it's difficult to be sure.
The last two files patched will need approval from a relevant component
maintainer.
More information about the Gcc-patches
mailing list