From 7526a5f7b68b49e362a0203b656ef2b24b15aa2e Mon Sep 17 00:00:00 2001 From: "H.J. Lu" Date: Tue, 20 Oct 2015 09:17:48 -0700 Subject: [PATCH 1/3] Add R_X86_64_GOTPCRELX and R_X86_64_REX_GOTPCRELX X86 instruction encoding supports converting some instructions on memory operand with GOTPCREL relocation against symbol, foo, into a different form on immediate operand if foo is defined locally. Those instructions are: call *foo@GOTPCREL(%rip) => nop call foo or call foo nop jmp *foo@GOTPCREL(%rip) => jmp foo nop mov foo@GOTPCREL(%rip), %reg => lea foo(%rip), %reg When PIC is false, test %reg, foo@GOTPCREL(%rip) => test $foo, %reg binop foo@GOTPCREL(%rip), %reg => binop $foo, %reg where binop is one of adc, add, and, cmp, or, sbb, sub, xor instructions. I am proposing to add 2 new relocations, R_X86_64_GOTPCRELX and R_X86_64_REX_GOTPCRELX, to x86-64 psABI. Instead of generating R_X86_64_GOTPCREL relocation agasint foo for foo@GOTPCREL(%rip), we generate R_X86_64_GOTPCRELX or R_X86_64_REX_GOTPCRELX if there is a REX prefix. Linker can treat them the same as R_X86_64_GOTPCREL or it can perform the transformations listed above. * object-files.tex (Relocation Types): Add R_X86_64_GOTPCRELX and R_X86_64_REX_GOTPCRELX. Generate R_X86_64_GOTPCRELX/R_X86_64_REX_GOTPCRELX instead of R_X86_64_GOTPCREL for indirect call/jmp, mov, test and binop. --- object-files.tex | 24 +++++++++++++++++++++++- 1 file changed, 23 insertions(+), 1 deletion(-) diff --git a/object-files.tex b/object-files.tex index 423fbc3..826783b 100644 --- a/object-files.tex +++ b/object-files.tex @@ -438,7 +438,7 @@ or \texttt{Elf32_Rel} relocation entries. \begin{table}[H] \Hrule \caption{Relocation Types} - \small + \myfontsize \label{tab-relocations} \begin{center} \begin{tabular}[t]{l|r|l|l} @@ -481,6 +481,8 @@ or \texttt{Elf32_Rel} relocation entries. \texttt{R_X86_64_TLSDESC} & 36 & \textit{word64}$\times 2$ & \\ \texttt{R_X86_64_IRELATIVE} & 37 & \textit{wordclass} & \texttt{indirect (B + A)}\\ \texttt{R_X86_64_RELATIVE64} $^{\dagger\dagger}$ & 38 & \textit{word64} & \texttt{B + A} \\ + \texttt{R_X86_64_GOTPCRELX} & 41 & \textit{word32} & \texttt{G + GOT + A - P} \\ + \texttt{R_X86_64_REX_GOTPCRELX} & 42 & \textit{word32} & \texttt{G + GOT + A - P} \\ % \texttt{R_X86_64_GOT64} & 16 & \textit{word64} & \texttt{G + A} \\ % \texttt{R_X86_64_PLT64} & 17 & \textit{word64} & \texttt{L + A - P} \\ \cline{1-4} @@ -517,6 +519,26 @@ in the GOT where the symbol's address is given and the location where the relocation is applied. \end{sloppypar} +For \code{name@GOTPCREL} in: + +\begin{footnotesize} +\begin{verbatim} + call *name@GOTPCREL(%rip) + jmp *name@GOTPCREL(%rip) + mov name@GOTPCREL(%rip), %reg + test %reg, name@GOTPCREL(%rip) + binop name@GOTPCREL(%rip), %reg +\end{verbatim} +\end{footnotesize} + +\noindent +where \code{binop} is one of \code{adc}, \code{add}, \code{and}, +\code{cmp}, \code{or}, \code{sbb}, \code{sub}, \code{xor} +instructions, the \texttt{R_X86_64_GOTPCRELX} relocation, +\texttt{R_X86_64_REX_GOTPCRELX} if the \code{REX} prefix presents, +should be generated, instead of the \texttt{R_X86_64_GOTPCREL} +relocation. + \begin{sloppypar} The \texttt{R_X86_64_32} and \texttt{R_X86_64_32S} relocations truncate the computed value to 32-bits. The linker must verify that the -- 2.4.3